I don't know which is doing it, the dog or the cat, but one of them has started urinating in the same spot by the back door. The dog spends lots of time outside and the cat has a litterbox. This just started. Both are adults and both hang out in that particular spot. What can I do or use to eliminate the pheromonal smell that gets left behind even after the area has been cleaned and disinfected? I can't think of another reason the same spot keeps getting used. Only one other possibility comes to mind. I used to keep a folded up cheap polar fleece blanket by the door to keep the winter drafts out and the cat snoozed there quite a bit. The blanket got washed and put up a week or so ago. Could this be a protest about the blanket being moved?

Sound like it could be. I have all dogs now, but I used to have cats too. Cats are much more likely to "get back at you" than a dog. I don't think it is in a dog's nature to be revengful. :). Altough if you have more than one male dog somethimes one will want to mark their place., even if they are neutered.

and cat urine is the one that permeates the house and lasts for centuries and is the strongest.... so that should help decide the culprit....

and get the cat checked for kidney/bladder problems

I searched and finally found the bottle of Urine Gone we bought when both were young. I sprayed the entire landing with it just in case. It says it has enzymes that remove the "smell". I think I'll put the blanket back just in case. If not, then they both go to the vet to see if one or the other is having some kind of urinary problem.

Put the blanket back and see what happens; maybe they were truly loving it in that spot. If that takes care of the problem leaving the blanket is a simple fix.

Is your cat still using the litterbox? Often a urinary tract infection will have a cat relating his/her pain to "the box" and avoid it.

We have "Out! Pet Stain and Odor Remover" from Wal-Mart. It works the best for us (we tried different sprays when we were housetraining). My dear mil can't believe we have our furbabies inside because our home doesn't "smell". :)

Taking them to the Vet. should be the 1st thing to do when something like this starts.
I have 4 cats now and have had cats for the last 2o years and never had one urinate in the house, can't say that for the 5 small dogs I've had.
If a dog spends too much time outside, they seem to get mixed up as to where they should go potty. I try to keep mine inside and let them out every so often to potty, this works out well for mine.

Your local pet shop will have a product for animal stain and odor remover designed especially for dogs and cats. You may also want to consider have the dog and cat checks for badder infections. etc.

You might try vinegar.

Nature's Miracle. Good stuff.

Did you change anything in their routine? Sometimes they are way more sensitive than we think. Did you change the litter? We did and found both boys doing the "I gotta go" dance at the back door (and assorted wet spots throughout the house)

Could be also a UTI for either - Nature's Miracle is the absolute best for these problems.