My 10 month old puppy is digging lots of holes too. I have tried the poo in the hole but he just goes elsewhere and digs another. I sprinkle the area with hot pepper but have to admit that I don't do it daily and then it rains and gets washed away. Maybe I will try the pile of sand trick. Someone suggested to me recently that I should bury a tin can in the holes as dogs don't like the feel of the tin.
Maggie