Perhaps you shouldn't let your cat roam free. Cats that are allowed outside have an average lifespan of three years, as opposed to 11 for cats that are kept indoors. Letting your cat outdoors seems rather negligent, seeing as how it exposes the animal to numerous hazards. Letting one's cat outside is a nuisance in an urban or suburban setting. Domestic cats wreak havoc on local songbird populations, as I found out first hand. Are you a specieist?
Love your cat; keep it indoors!