You can't blame cats for digging up your bulbs. The kitties are merely looking for a nice, soft spot to relieve themselves, and the loosened soil around newly planted bulbs fits the bill quite nicely. Chemicals such as garlic and red pepper can help but have mixed results. The best way to keep cats from digging up your bulbs is to create a physical barrier.
Using clippers or scissors, cut circles out of chicken wire, about 8 inches to a foot in diameter, depending on how big the bulb hole is.
Position the chicken wire over the spot where you have planted your bulbs and gently nudge down into the dirt with your fingers, pressing it to a level fit.
Stake down the circles with small metal garden stakes and cover lightly with a thin layer of dirt. The chicken wire has enough room for the bulbs to send stalks up into the sunlight, but not enough for kitty to do some serious digging. Cats don't like to walk on chicken wire, so your cat will naturally avoid the area.