Head lice is manly found/picked up by little kids in sand but you can get it from grass with sand in it and trees with lots of birds might have some lice on the nest but as far as I know they are both safe areas as long as no sand or animals are contributing. Animals are really the big deal though because the lice has to have something to live off of and the sand is so bad because animals lay there for warmth and cats like to poop there. If you have a backyard with minimal animal contact there is less of a lice chance.