I sometimes do work for a commercial tree service and poison ivy ranks right up there with electrical lines and stinging insects on my list of least favorite occupational hazards. I carry a box of individually packaged IVY X towelettes. Wiping down within a few hours of exposure usually prevents it for me. They are also great for wiping down chainsaws, weed trimmers, and guns. If you're extra sensitive to the urushiol, use the wipes immediately after exposure and then shower with Technu as soon as it becomes feasible.