Man I hated getting into these whenever we would be walking across a pasture from tank to tank fishing. Burn and itch for 30 minutes.
I'll tell you how to get rid of the pain and itch immediately... and NO, it's not taking a leak on it.
These things grow in dry, sandy conditions. So when you run into one, look around for the nearest exposed, completely dry sand. Get a hand full of sand and RUB. By the time the sand has gone through your fingers, the spines will be out of your leg and it'll stop stinging and burning.
My aunt showed me how to do this when I was somewhere around 8 years old. It works.