We had this problem in our previous garden. They ate over 5,000 tulip bulbs and did a lot of damage digging them up. First of all, you have to find the point/s of ingress and block them off. We used ordinary chicken wire for that, but it should not be stretched tight as they will climb it. We found that if it was loose so that when they climbed it , the wire bent over outwards (hard to explain, they could not get over it.
If they are digging their way in you need to bury chicken wire flat along the ground top at least a foot outwards. Again hard to explain.
We also heard (Prince Charles’ gardener) that half empty plastic tonic water bottles placed along the fence line stopped them. We also hug strips of cloth soaked in Jeye’s fluid on the fence. The small is supposed to keep them away, but it obviously needs renewing regularly.
Hope you manage to stop them.