In my limited experience, kitty litter frightens rabbits but doesn't bother skunks in the least. Your choices are to trap or kill the animal, or to fence it out, or to discourage it from thinking of your place as a nice safe comfortable haven.

Radio Shack sells a little battery operated motion sensor alarm that works great to discourage dogs from countersurfing or turning over the garbage can, not very expensive - maybe you could rig up something like that.