Something keeps digging a huge tunnel under the concrete slab of my garden shed. I’ve tried filling it in, but it’s back every morning and I’m worried the foundation will crack. What would you do?

Finding a hidden tunnel beneath the concrete slab of your garden shed can be a confusing and stressful discovery. It is completely natural to feel a mix of curiosity about what is living under there and a genuine fear for the safety of your building. A tunnel might look small at first, but these underground pathways can actually weaken the very foundation of your shed. If you don’t take care of the problem quickly, you could end up facing very expensive repairs for a cracked or sinking floor.

In this guide, we will walk you through a clear, step-by-step process to fix this situation. We will help you figure out which animal is digging and show you how to protect your property for the long term so you can finally have some peace of mind.

1. Confirm It’s Really a Groundhog (And Not Something Worse)

Before you start any work, you need to be sure about which animal has moved in. Groundhogs, which many people call woodchucks, are famous for being expert diggers. They build very large and complex tunnel systems. Usually, a groundhog hole is about 6/1 to 1/1 foot wide (which is 6 to 12 inches). You will often see a large pile of dirt right outside the opening.

However, other animals like skunks, raccoons, or armadillos might also be the ones responsible. To be sure it is a groundhog, look for paw prints that are about 2/1 to 3/1 inches wide with five clear toes. Many homeowners also find it helpful to set up a simple “trail camera to capture the nocturnal activities” of the visitor. Identifying the right animal is the only way to make sure your plan will actually work.

2. Understand Why Groundhogs Love Your Shed Foundation

It helps to think like a groundhog for a moment. They aren’t trying to annoy you; they are just looking for a safe home. Your garden shed provides a perfect roof that stays dry and protects them from predators like coyotes or large dogs. Plus, if your yard has a garden or plenty of grass, they have a “bountiful food source” right at their doorstep.

Groundhog homes are not just one simple hole. They are designed with many different rooms and tunnels. They use these spaces for sleeping, raising their young, and even as a bathroom. By understanding that they are looking for safety and food, you can start making changes to your yard that make your shed look much less inviting.

3. Assess How Much Structural Damage Your Shed Could Actually Suffer

The damage from a digging animal can go from a small nuisance to a total disaster very quickly. While you only see one hole, the tunnels underneath can be anywhere from 8/1 to 66/1 feet long. They can also dig as deep as 5/1 feet down into the earth. When that much dirt is removed from under a concrete slab, the heavy concrete no longer has anything to sit on.

This can cause the foundation to crack or shift. You might notice that the shed door doesn’t close right anymore, or the whole building looks like it is tilting to one side. It is very important to check your concrete often for “visible cracks, unevenness, or gaps between the slab and the shed structure.” Catching these signs early can save you thousands of dollars in construction costs later on.

4. Stop the Nightly Re-Digging With Immediate, Temporary Fixes

If you see the animal digging every night, you need to act fast to stop the progress. A great short-term fix is to place very heavy rocks or large paving stones directly over the hole. You can also use a strong metal screen called hardware cloth to cover the area.

If you use wire mesh, make sure you bury it at least 1/1 foot deep into the ground. You should also let the mesh extend outward away from the shed. This creates a floor that the animal cannot dig through. These are “meant to be short-term solutions” while you figure out a more permanent way to move the animal away.

5. Use Humane Harassment Tactics to Make the Burrow Less Appealing

You don’t always have to use traps to get a groundhog to leave. Sometimes, you just have to be a bad neighbor. Groundhogs hate being disturbed, so you can use “humane harassment tactics” to encourage them to move out on their own. Motion-activated sprinklers are great because a sudden spray of water will scare them away without hurting them.

You can also use scents that groundhogs dislike, such as predator urine or special store-bought sprays. Some people find success by placing wind chimes or vibrating stakes in the ground near the hole. The goal is to make the area so noisy and smelly that the groundhog decides to “naturally seek a new location” that is much quieter.

6. Deploy Live Traps the Right Way (And Check Local Wildlife Laws)

Sometimes a stubborn groundhog just won’t leave. In this case, you might need to use a live trap. A good trap for a groundhog should be at least 1/1 by 1/1 by 32/12 feet (roughly 12 x 12 x 32 inches). Place the trap right near the main entrance and use tasty treats like fresh lettuce, carrots, or sliced apples as bait.

Before you set a trap, you must “check local wildlife laws.” In many places, there are very strict rules about where you can release an animal or if you need a permit to move it. It is also your responsibility to check the trap several times a day to make sure the animal isn’t sitting in the sun or rain for too long.

7. Seal Off the Burrow Safely Once You’re Sure It’s Vacant

Never seal a hole until you are 100% sure the animal is gone. If an animal is trapped inside, it will suffer, and it will also cause a very bad smell under your shed. Once you are sure it is empty, fill the hole with a mix of gravel or a special soil-and-cement blend that gets hard over time.

To be extra safe, cover the filled hole with heavy-duty metal mesh. This mesh should go 1/1 foot (12 inches) deep into the ground to “discourage future digging.” Taking this extra step ensures that a new animal won’t just dig out the loose dirt you just put in.

8. Install a Dig-Proof Barrier Around the Shed Perimeter

The best way to handle groundhogs is to make sure they can never get under the shed in the first place. You can do this by building an underground fence around the entire perimeter of the shed. Use galvanized wire mesh and bury it 1/1 foot deep.

A pro tip is to bend the bottom of the mesh outward at a 90-degree angle to create an “L” shape. This is called a protective apron. When an animal tries to dig down, they hit the metal and give up. This barrier should also come up about 2/1 feet (24 inches) above the ground to keep them from trying to climb over it.

9. Reinforce or Repair the Slab Before Cracks Become Costly

Once the animal is gone and the hole is sealed, you need to look at the concrete again. If you see small cracks, you can usually fix them yourself with a “concrete patching compound” found at any hardware store.

If the damage looks bad, you might need to add more concrete or use steel bars to make the slab strong again. “Regular maintenance and inspections” are the best way to make sure your shed stays standing for many years. It is much cheaper to fix a small crack today than to replace a whole foundation next year.

10. Change the Yard Conditions That Attract Groundhogs

If your yard looks like a groundhog paradise, they will keep coming back. You can make your property less attractive by keeping your grass cut very short. Groundhogs feel safe in tall grass, so taking away that cover makes them feel exposed. You should also clean up piles of wood or old debris where they might hide.

If you have a vegetable garden, make sure it has a strong fence. You can also try “planting groundhog-resistant plants” or using natural items like garlic and hot pepper spray to protect your favorite flowers. If there is no easy food and no place to hide, the groundhogs will go somewhere else.

11. Know When to Call in Wildlife Control or a Structural Pro

There is no shame in asking for help. If the groundhog is too smart for your traps, or if you see huge cracks in your concrete that look dangerous, it is time to call a professional. A wildlife expert can “safely and legally relocate the animal” without you having to worry about the laws or getting bitten.

Likewise, a structural engineer can tell you if your shed is still safe to use. Spending a little money on a professional now can save your “property investment” and give you the confidence that your shed is secure.