A ball or tug can be placed on the ground or hung inside the blind, you can show the dog and pull him back out of the blind to create drive and then send him in for his toy. The next step is to have the dog on a sit stay, put the ball in the blind, then send him, you can also give the dog another ball when he gets back to you. After many repetitions, you can remove the ball from the blind and just reward him when he gets back to you. By ensuring that he gets another toy when he gets to you, he should stay tight to the blind.
You can use mini-blinds, home made blinds, or other items to teach a single blind, then do more than one, you can place all the blinds in different places to teach the dog to go to a specific blind. The more repetitions you can do gradually increasing the distance, the better. Once you begin doing blind searches in protection, you can continue using balls or place helpers in different blinds to keep the dog guessing.