Well, his hutch is already as close to the house as it could be - and it's up on stilts with both a closed section and a wire mesh, so I don't think there's anyway it could get him aside from pushing the hutch over, which would be nigh on impossible. It doesn't come very often (as in the stamping only occurs sporadically, and it has been happening for quite a long time), but this is the first time we found droppings. Surely a fox would just give up and find easier pickings? There are plenty of dustbins etc around here, as well as other animals in hedgerows, I'm sure.
The rabbit comes in to the house every day and his general health seems good, so I don't think it's affecting him too much/at all, although I am aware they are sensitive creatures and can go into shock very quickly/easily.
Also sorry Carrot, but "snapping their spines through stamping"?! How does that happen, and what about wild rabbits who use stamping on a daily basis, surely? Anyway, everyone thanks for the suggestions; I think if we see any more droppings (because I took this as an overt sign of intimidation) then we might try something to scare it away.