If you know anyone who can give you large rocks you could line your side of the fence with the large rocks and push any into the holes they dig.
How to keep neighbor dogs from digging under fence.
First eliminate attractions to the dog to your yard.
Installing a chicken wire under the fence.
You can stop your dog from digging under the fence through redirecting to a sandbox placing chicken wire under the fence hammering another fence layer into the ground or decorate your yard with dog friendly bushes or heavy stones.
Causes of dog digging.
For a bigger dog you may go with a foot apart or more.
Collect your dog s droppings from around your yard and place them in common spots where they tend to dig.
Chicken wire can be dug into the soil under the fence up to an estimated 2 feet.
Your dog will stop digging in that spot since they don t want to paw through their own droppings.
Big jars of red pepper flakes from the dollar store might deter them a bit.
If the fence is made of chicken ire it can be bent into an l shape which goes into the soil.
Determine how far apart your spikes rods etc need to be to prevent the specific animal from passing through.
For instance if you have an adjoining fence of 50 and your neighbor s dog is a medium sized dog then you might choose to place your stakes about 10 apart.
But you would have to replace them after every good rain.
If you can t find an agreeable solution with your neighbors then you can have several other steps you can take.
The best way to keep a neighbor s dog off your property is for your neighbors to keep their dog off.