Schedule 40 is stiffer and will last a whole lot longer than fence posts. But, it will still sway in water over 6' deep if not cross braced.

Try augering it in, and try sticking a hose down the pipe without an auger on the end. The pipe might just slide down into the pond bottom as the flow of water washes away the dirt from under the pipe.

There are brackets specifically made to clamp on the pipe and have a 90� fitting for another horizontal pipe.

I have used brackets like these:


and brackets from Tommy Docks to build docks and both work well. http://secure.tommydocks.com/parts.asp?choice=parts&page=main


www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).