Have you built a set of boards that seem to bounce every time you hit the middle of the board? There is a way to fix this problem without taking the set apart, and it is rather easy. You can simply use a two by four as a cross-brace underneath the box. Many builders use this in the design of their boards. The board should be placed about half-way in between the hole and the bottom of the board. This design fixes the bounce-effect very well, no matter what type of boards you have. It works for three foot and four foot boards alike.
One way to prevent this from the start is to use a thicker surface board. Most people seem to use half-inch plywood in the construction of their boards. Half-inch plywood does allow the bags to bounce, but it also depends on the quality of wood and how well the set is put together. I would recommend using something a bit thicker than half-inch plywood. 3/4 inch plywood works and almost allows for no bounce at all. The ACO uses something in between (5/8" with a small cross-brace), and it seems to reduce the bounce a lot.
In my opinion, I think it is better to allow the bag to bounce a little bit. It can be a useful shot if your opponent's bag is right in front of the hole. Sometimes you can bounce right over it and make it in the hole without moving the other bag. Bouncy boards require more accuracy because there is not as much leeway for an inaccurate shot.