Cats can also be prescribed antidepressants for urination issues. An indoor-only cat might do okay as a barn cat. If you do give him to a shelter, disclose why to the shelter. If you do not and someone adopts him and he pees, they might not act in a responsible manner and might toss him or if they do put him back in the shelter, he might get put down. If you do take him to the shelter, realize that he might get put down. Is he a particular breed or a plain old domestic short hair? I ask because there are rescue groups for just about every breed out there. I volunteer (and adopted both of my cats) from a Siamese rescue. Likely he is feeling the need to define his territory due to the kids and maybe there was a smell on the bag that he didn't like. Didn't have to be an animal smell even. I am not to the degree that some of my rescue friends are (some feel you should NEVER give your animal away). I can understand that there might be circumstances in which giving him away is the only choice but hope that all the options can be looked into before you do. It seems as though you've done a lot of work on this and I commend you for that