Advice on how to stop burrowing into neighbours??

Hello.... I'm asking for someone else. She wants to pur a large enclosure against her fence but is worried they will burrow through to next door. Any advice on how to prevent this??

I’d suggest she puts it on a concrete base, uses paving slabs to create a solid base, or use weldmesh with turf on top. If she is worried about them actually going through a dividing fence I would suggest she has a 4th side for the run made of weldmesh rather than using the fence as a 4th side.