Get some cheap 20 to 30 lb. test mono from Walmart known as Omniflex, and some furring strips from the lumber yard to make the stakes. You don't need many if it's a straight line. Use some dry wall screws to attach the line. Set one line low enough they can't get under it and one or two above that. Basically you want to set this up so they can't wade into the water and it's too deep on the water side to land. I've actually put two parallel staked lines in also when the water is shallow.
Bottle rockets can be persuasive as is a paint ball gun.. Be aware they can show up at night but will show up just about anytime although morning and evening are their favorite feeding times.
I cringed when I saw your photo of the skewered rainbow. Been there done that!
