How to get my cat to stop pissing and pooping on my carpet.. help?

My 9 year old male cat is not using his litter box as often, and is pissing and pooping in the same area in my basement on the carpet. How can I fix this problem? I am holding out on taking him to the vet, because the vet in our town isn't very good, and they tend to wnat to sell you every thing which is aggrivating. I can't squirt him with a bottle, because I don't catch him in the act ever... I only smell, feel and see (poop) the evidence after he is done. Please help before my husband puts a bullet in my cats head and fixes the problem himself.