You have a couple problems to deal with. The first being the rocks, but second the minimal range is huge. Hay bales will not slow the arrow enough to stop damage unless it is very compacted/dense. Most people do not have access to a true 100lb bale, and any lighter will not have the density needed. They also break down, and after a year or so loose density. Oh, don't forget if you hit a gap the arrow is going through at almost full speed. I have used a sytem of carpet, but it will probably damage your fletching at 25yds depending on arrow KE. Make a 2x6 frame and hang carpet on each edge of your header. The gap really slows the arrow before hitting the second layer. If you made a third layer by using 2 -2x4's as a header it might work better. I only used two layers, and never had a problem with 40+ yd shots. If nothing else shoot rubber blunts into a single layer until your skill improves. By using one of the block style targets you should not need a back stop for arrow protection at 25yds after your skill increases. Most people with todays new equipment don't shoot at the same POA under 30 because of arrow damage. You will understand in very short order.
