Whats the best way to level low spots in yards? Say the yard is pretty nice, but has a couple spots that are maybe 3-5' diameter, and are 2-3" lower then the rest of the yard. Should I just put black dirt in these spots and let the grass below grow up? Maybe toss alittle seed in it to? Or do I have to dig up the grass below and then add black dirt and reseed? Thanks guys!