Thank to Marcus who had a bit of sonotube left over, got over Bunnings with a mate and his ute to pick up 21 bags of quick set and yesterday morning got reo and lot of steel for the pier. Today I marked with an X where I wanted the pier, clear of everything and stuck a long fencing pole in it right through a 19mm tubing of my irrigation system. I mean... wtf? My backyard is approx 13x10m and there's only one line going though the middle and I manage to pin it dead on... So I spent the first hour fixing leaks. Happy with the progress now. Down 600mm by 400x400mm. The clay is like butter. The ground is wet and moist really deep. Easy to work with.
I've done that as well - managed to cut right through our own main waterpipe while digging a post hole. There was water everywhere, hilarious! At least now I know where the water main is
I must have a knack for finding piping. Couple of years ago I went through a gaz pipe (twice - one up one down) mounting a wall bracket for a plasma on a wall. I wasn't drilling but I told my mate where I wanted it.
So if any of you guys need a stud finder, electrical or gaz line detector, water main, sewerage pipes etc... just drop me a line and don't listen to a word I tell you.
PS: I don't do petrol or gold. Only serious queries.
So I spent the first hour fixing leaks. 
Happy with the progress now. Down 600mm by 400x400mm. The clay is like butter. The ground is wet and moist really deep. Easy to work with.
