A simple pond screen frame can be constructed from PVC tubing. PVC is lightweight, durable, and waterproof. It can also be painted to match the area around your pond and minimize the frame's visibility. Pick up enough straight PVC tubing material, and PVC glue, along with the necessary elbows to make the turns and transitions around your pond. Dry fit the whole frame together and place it around your pond prior to gluing any of the pieces. If you want to be able to take the frame apart for storage, opt for drilling and bolting the PVC tubing to the elbows.
Screen can be easily replaced, and thus you should not spend too much on it. A season or two will leave it filled with leaf litter and debris, as well as stretched out and in need of replacing. Look for screen material intended for re-screening window screens in your local home improvement store. If you cannot find a roll that will cover your frame in one piece, two or more strips can be laid next to each other and sewn together using a needle and fishing line. Secure the screen by wrapping it around each end of the PVC frame and screwing it to the PVC using a screw with a washer, with one placed every 6 inches around the circumference of the frame.
Stakes and Tie-Downs
Secure your pond screen around your pond to keep it from lifting up and away in a storm. This can be done cheaply, though not attractively, using a few bricks on each corner. If you want to make your screen look somewhat less unattractive you can use tent stakes and zip-ties. Hammer the stakes in to the ground and secure them to the pond frame using the ties.
Notes on Construction
Be sure that your screen does not sag below the waterline when your cover is placed over your pond. This can prevent fish from surfacing for air, and cause them to drown. If your screen does sag, replace the screening, tighten it up, or raise it up by placing bricks or pond stones under the frame. After a season or two, the screening will sag and begin to fray, replace it immediately. If animals such as raccoons are especially bothersome in your area, you can replace your screening with wire mesh for more security, though with added material cost.