I've always had problems with this - foxes are the current issue, but cats too. There is the poo, obviously, but the main issue is digging holes and disturbing plants in the process. This latter has been a daily issue recently. Anyway, I'm interested in what others have tried.
The main thing that has worked for me is dense planting. They love bare soil. So that is my ultimate strategy!
When I've got patches of bare soil the most effective thing has been rose pruning clippings scattered over it. You can buy black plastic mesh with prickles which you peg down - better for large areas but costs money and can be a pain when you forget to remove it and plants grow through it (chicken wire would do the same) - but prickly clippings are very effective.
I've got one of those electric scarer things too but am not convinced it really makes a difference.
I know to some this will sound a bit sad - it's nature, let them do their thing yadda yadda - if that's fine for you then great. Personally I'm fed up having stuff dug up and would love to see some of the birds that nest in my hedge successfully raise a fledgling or two before the cats get them.
What have others tried?