Jscummy,

Sounds like your configuration will work for a siphon. I also like that you are using 4" pipe.

I agree with gehajake that using a check valve on the pond inlet side will make your life easier.

The low pressure type that you need is usually called a "backwater valve". You should be able to find one at a big box hardware store. I see $33 at my local Menards and $58 at my local Home Depot.

However, be advised that the female connections on the backwater valve are made to fit DWV pipe. Are you using PVC schedule 40 for your siphon pipe? If so, note the type of pipe you are using and test a piece of that pipe at the hardware store to make sure it fits your backwater valve. (I have had fittings NOT fit the pipe when trying to mix large diameter SCH 40 and DWV pipe.)