I have two cats .I am pretty sure my 5 year old neutered male cat has been spraying in a few spots like doors, washingmachine etc. Today i found a puddle of urine on the laundry room floor. The only reason i can think of him doing this is that I noticed that a strange cat had been coming in through the cat door. I noticed him leave one night and locked the cat door ever since. The cats still go out i just let them out myself. Could this be reason enough? stress or smells in the house are triggering him to do this?