It was a really bad rash above his knees and on his arms, between his wrist and elbow. It looked just like a poison ivy rash, but we have no poison ivy here. He was clearing a bunch of stuff, so no telling what it was. I've been trying to narrow down the search, and identify some mystery plants, all at the same time. It's weird that it was above his knees because nothing touched his skin there. He did kneel on the ground, but the area above his knees wasn't touched directly by any plants.
We've always had pets, and I'm positive that it wasn't caused by them. Haven't changed anything other than where we live. It has to be a plant somewhere!