Hi,
Some further advice to assist those who love ponds. Pond plumbing for instance is not like Pool plumbing.
Pump Principles for Your Pond

http://www.aquaart.com/pumps.html

Other Pond Links:
http://www.peteducation.com/category_summary.cfm?cls=16&cat=1917
http://www.koicymru.co.uk/navbar1.htm
Heres's a bit of sage advice from the main article:
Remember, a pump can’t pump out water if there isn’t any available. Even if your supply line comes up and over the top of the pond wall, it will still offer a flooded suction if it has no breaks to atmosphere before it goes back down below the surface level.
Regards,
Tango