Outdoor cat has whole yard, but pees and poops at back door

by Tom D.
(Fort Lauderdale, FL)

We live in a quiet neighborhood with a dead-end surrounded by canals. Our cat has the whole backyard to pee and poop in, including sandy, earthy patches that are litter box-like.

However, for the last couple months, she's been peeing and pooping exactly at the back door threshold. Essentially we have to play hopscotch to get from the backdoor to the pool area and vice versa (Mexican tile that basically channels the urine 5 feet across the patio to the pool area, leaving the poop sitting by the door).

I've ruled out medical issues and the only thought is a new neighbor's (just found out it wasn't a stray) black Manx that sometimes comes in our back yard. I think she is trying to ward the other cat off by claiming the patio (where she's fed and given water) and basically claiming us humans as all hers.

If anyone agrees with this diagnosis, what can I do to stop this because it's causing us to track urine and occasional poop smears into the house.

Originally there was a mat, which I tossed. Then I cleaned with vinegar and water, but she still persists to do it. Thank you for your help!