My little boston terrier periodically marks territory. He has been neuterd and he is three yrs?

is three yrs old. I just noticed that I hung new draperies and he marked them. I have just built a new house lived her for 7 mo. I noticed he has marked my bedroom suites leg and a couple times my covers for the furniture. I have caught him with the covers so he hasn't anymore but it is hard to catch the little burger,yes I have another male dog but he doesn't do that. When I first got him he wasn't neuterd and he did it all the time. But within a week after I got him I had him neutered. Three times in 8 months he has marked covers and drapes?????????