Dogs digging up garden or fox?

It most likely to be foxes they dig for grubs and worms ,try a prickle strip not harmful them but they don't like walking on them there is sprays you can use also a high pitch sonic alarm works try everything hope it helps nick

Put a fence all the way round it,, how big is the garden

Remove the pest in the lawn by applying a nematode soil drench or selective soil drench. This will stop the digging to feed.

In my experience its not Foxes that dig its Badgers. Foxes tend to foraige on kitchen waste.But first you need to confirm the animal if its a fox the poo has a very pungent smell which you wont want on your hands or clothing If your an animal lover the best way to divert the badgers attention is feed them. Do it regularly at a set hour say 9-10pm, in the same place and they will become an amusement. Alternatively a product called Grazers sprayed on the boundary will keep many wild animals from your property, or block the regularly used point of access used to your property there will be foliage damage as evidence. Grazers sprayed on a six week cycle will keep most animals out. I witnessed a beautiful garden backing onto a open field with many rabbit warrens but there was no evidence of rabbit invasion. A cheaper option is to remove the food source use water with diluted washing up liquid in it. Leather Jackets etc will then surface and birds will remove them.