Hi guys, 
My Border Collie pup is 4 1/2 months old.  He has a fetish with digging.  I have tried a lot of tips, but nothing seems to work.  I exercise him with hour walks twice a day, he has heaps and heaps of toys, a digging pit that I bury things in, but he doenst like it.  I put bricks in the holes where he digs, but he pushes them aside, he seems to like it better with a brick. (hehe)  I tried faeces in the holes and citronella.  He digs all the time, whether I'm home or not.  I catch him in the act often and dicipline him, he seems to know he is doing the wrong thing, I lock him up for time out for a while, but as soon as I let him out he's back to digging. I train him often, with everything else he is very well behaved.  With any thing else, if I discipline him he stops straight away.  There are some dogs next door, and often the holes are along the fence line, maybe he is trying to get to them????  But I cant really keep him away from that side of the fence.  Does anyone have ANY other suggestions.  PLEASE HELP, my garden needs me. 
Thanks guys