I have tried using cat repellent sprays before and found that they either don't work or you have to spray it so often that it isn't practical. Don't know anything about the poo idea, however if the rabbit hutch is outside (next to or by a path) is there a grassy area there? With watering access?
If so, there are motion activated sprinkers available which could discourage, but not harm your cats from focusing their attention on your neighbours rabbit.
They shoot jets of water (which you program the length and width) over a predetermined area thus discouraging animals from approaching.
Just an idea
