Strange cat behavior

One more thing to add to yesterdays saga. When we were coming in from the yard that evening, and Mickey shot out the door. That isn't something we usually worry about with him. He normally has no interest, and if he does go out, it's just to rub on your legs, and ask for dinner, and he's quite amicable to being gathered back inside. Not today. He ran along the edge of the house keeping out of reach as though we were terribly frightening and strange. Then the weirdest part. He broke away, ran straight to a pile of dirt (our garden is in-progress) and immediately began peeing on it. Not marking, just regular litter-box behavior, except he seemed terribly concerned about us being near and watching him. We took a step too close and he was off again. Eventually we herded him back inside, where he was completely fine again. We were still wearing clothes from the shelter visits, but he'd been happily cuddling with us in those clothes earlier in the day. The behavior could have made sense he was going after a bird or something, but apparently he just desperately had to use a new litterbox? (the regular litterbox was in fine shape). Cats are strange.