I wanted to find out. I had an Osage Orange tree that I grew from seed that I decided to experiment on. It's one of a number of trees I'm growing in root pots in a spot on the lawn. I decided to try my urine experiment on one particular tree. It's may be coincidence, but the one I peed on every day for the last week or so is the only one that got snipped off by rabbits recently. In fairness, it is on the outside edge, but so are many more of the trees that weren't snipped. Granted this is a tiny sample, but as near as I can tell, if urine had any effect at all, it attracted a rabbit attack. YMMV.
The deer ate all but one leaf off of my weeping mulberry tree. So I had my husband go pee on it. He's been peeing on it for a month whenever he's in the area. Not only did the deer stop eating it, it's grown more leaves in the past month than it had in it's whole 3 years of life. A win-win for me!
I tried to get my son to help out and pee on it, too, but he doesn't want to. Well, he did the one time we had people over, but I told him NO, we only pee outside when no one else is around!
I think it is highly dependent on the species and the location. We have deer that are used to human scents because we live right next to a subdivision with small lots, and they browse in there because it is safe and food is plentiful. Urine may be a little more aversive than other scents, but they don't care. My squash patch doubled as the outdoor urinal and they completely obliterated it last week. If the plants have verdant foliage due to the minerals and nitrogen, they taste like candy to deer and rabbits, so I think it can even backfire depending on the specifics.
I remember Joseph Lofthouse (I think) saying that excess nitrogen brings in aphids to effectively "bleed" the plants. I think there is an element of that with other browsers, they seem to be able to smell the rapid fresh growth.
Standing on the shoulders of giants. Giants with dirt under their nails
In my experience, human urine doesn't protect plants from nibblers. That's not to say that it isn't useful, just not that way. In my experience, wildlife varies so much from place to place that these kinds of generalizations just aren't that useful. I was told that foxes are shy, yet we have at least one of our property that when they see us, they look at us like, oh, you want to get in here, or over here, let me finish what I'm doing and I'll get out of your way. It's disconcerting how little we bother it. But I'm sure it's not that way everywhere.
Living a life that requires no vacation.
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Permaculture Technology Jamboree: June 29th-July 10th, 2020, Wheaton Labs