You don't say what kind of deer they are. If they are one of the smaller in stature kinds such as Muntjac, you might be able to build up thorny barriers etc to help deter them, but this won't work with the larger kinds. Have you seen how high deer fencing is in the Highlands? You might have some success with hanging CDs or something which flaps about like pennants of material.... Perhaps reminders of human scent would help too as most deer are very nervous of humans.
Whatever you try, good luck with it!