If the urine is still wet, blot as much of it up as possible. Once that's done, or if the stain was dry when you found it, do this: In a mixing bowl, combine ½ cup warm water, ½ cup white vinegar, and ¼ cup Seventh Generation dish soap. Use a hand mixer and whip it into a frothy foam. Apply foam to upholstery and work it in with your brother's toothbrush. Scrape the nasty foam away with a rubber spatula. Use a clean damp cloth to wipe the spot. If the odor is not completely gone, you may need to risk spraying the spot with straight vinegar. The urine has probably worked it's way into the fibers, spray enough vinegar to do the same and pray for the well being of your futon.