If a male dog is fixed can he sense that there are other animals in heat and mark his territory?

Maybe he is marking his territory. Speak to your vet and see if this is the case or maybe a little infection is going on in his urinary tract system. Does he pee in the house or is it just outside? Male dogs I have found feel the need to pee far more often than their female counterparts. Hope I have helped.

Both male and females continue to mark their territory after being fixed. You need to post more details for a better answer.

I can sympathize! I have a 9-yr. old male poodle who was fixed when he was 7. I got him shortly after from poodle rescue. He marked in the house - on my dirty clothes bin, the toilet and bathroom rug, and furniture by the doors. I closed off rooms, watched him closely, put belly bands on him, took him to the vet, etc. I cleaned up the places with lots of enzymatic cleaner and kept it damp as instructed. I read every book and online article I could get my hands on. I take him for walks twice a day and encourage him to mark on trees, posts, and walls. He has a routine for going out for potty breaks. He will still mark by the door infrequently. I have been told my more than one person that it is a long-established habit and will take years - if ever - to stop. Good luck!