Cat Losing Hair on Back?
I agree with the answer above, you need to see a vet. In the meantime, have you checked him/her for fleas ? Have you noticed a change in behavior (excessive licking, scratching where the hair comes off...) ?
Cat Spraying Everywhere?
Unfortunately, neutering is the solution. Full adult male cat will spray. The more they do it, the harder it is to prevent them from doing it.