I had to resort to nailing chicken wire over my flower garden(it was covered by the walkway overhang so always nice & soft & dry) as the neighbour's cats were always digging up my bulbs. It wasn't fun trying to plant seedlings through the wire mesh, but it kept the peace. Our dog would go crazy when he'd see the cats, but alot of the time, the cats came at night.
I have heard that the crystals used for toilets/urinals or mothballs will also deter them, but they might be poisonous.