bugeye,
Do you want electricity at the pond, or aeration at the pond?
If aeration, it is generally much cheaper to run air line compared to electric wire. Also, if it gets cut by somebody working your ground, there is no risk of harm.
If electricity, you need to calculate your expected draw from all of the equipment that might be operating at the same time. Use a calculator (or a good electrician) to determine the voltage drop over your distance for that draw, and then use the smallest (cheapest) wire that will have an acceptably small voltage drop over that distance.
You may be able to hire an electrician to do the connection where you come off of your existing power and to do the connection and outlets at the pond. He could do the calculations for you and tell you exactly which wire to use for code, and how to leave it for his connections.
Will your line run through easy ground or difficult ground? (Rocks, tree roots, etc.) If easy, you could probably rent a riding trencher and do it yourself. The rental for a Ditch Witch RT45 is $300/day in my area.
