I have a slope and my fence installer only dug down into the clay hardpan 1.5 feet for a 6' fence. He put concrete in the hole but I think it's way too shallow. Since the land slopes I am thinking of building the area up with soil around the posts which would add the needed depth but I don't know if I should use concrete around the posts, since it would need to bond to the concrete just poured this week. Any ideas? Make a shorter fence or pull them out and start again?