try full strength vinegar....I saw a stronger one at Lowe's..........when you pull the mushroom dump it in a bag don't lay it on the lawn as the spores inside it will come out.........pour vinegar right into the opening....put a stick in the ground to see if that comes back....it might kill some grass....if you have an old mustard or ketchup container put the vinegar in that to control the dripping of the vinegar.....if that does not kill them. You can buy a mix or spray for fungus. Mushrooms are a fungus.