Hi Dogforum,
I am a new member, but not new to dogs. I have had several different breeds/mixes over the past 25+ years, including pitties, German Shepherds, terriers and our current 3 resident dogs. Ruben (possibly Dachshund and Jack Russell or Patterdale mix). Charlie (Italian Greyhound mix), and Pilar, our Chihuahua.
Ruben was the first of the 3. We adopted him in 2010.
I volunteer at a county animal shelter and Charlie was a favorite among the volunteers at the shelter, but he is a biter. If he does not know you well he bites. And it takes quite a while to get to know him to the point where he does not bite. I did not foresee a good outcome at the shelter for Charlie so I adopted him.
From the get-go he and Ruben butted heads. They rarely get in a scrap, and when they have neither has been hurt, but they are not thrilled with each other.
They are both neutered and housetrained and both approximately 6 years old.
I don't know if this rivalry has spawned an incessant 3 years of marking territory or if it is other factors. But they have not stopped marking in our house in the 3 years that we have had Charlie. I think the primary culprit is Charlie, but I am not eliminating Ruben as a suspect. We rarely catch them in the act.
We have had the carpet professionally cleaned multiple times and have tried about every enzyme/cleaner/odor eliminator we could think of to remove the scent so they will not re-mark. We use a belly band with pads on Charlie sometimes to reduce the amount of marking (and when he does wear it we do not see any marking, which leads us to believe that it is mostly Charlie doing it). While the belly band helps reduce the marking, it is not a practical long term solution and probably not too comfortable for Charlie.
My husband and I try to give each one the same attention so they will not be jealous of each other, if that makes any difference.
The vet wanted us to try Prozac at one time for Charlie to see if it would help with the biting/nervousness. We did not see any improvement in marking during that time (or biting for that matter). I am just mentioning that because some people have recommended that we try Prozac.
I'm sure this is a very common topic on this site, but it is one I really have not had to deal with before.
As for Pilar, the Chihuahua, she is spayed, approximately 15 years old and the most well behaved little angel of a dog we have ever seen

Any advice would be greatly appreciated!