My goats love docks all the time, we have a red rockie (rockie do have a website but you should be able to get it at any farm store) but our sheep can't get to it for reasons already mentioned.
How old are they? Are they having any goat feed?
treat wise, mine will do anything for a biscuit (not chocolate) - custard creams, digestive, rich tea...! bindweed, bit of willow, slices of fruit or veg, bread crust, few bits of dried pasta...