made a few backyard courses in my time, maybe i can help here.

pallets alone do nothing, you can stack 2 together and the paintballs wont get through though. Some other great things for bunkers are large sheets of plywood, dug out ground with a few 2x4s on the top, barrels if you got em, tires if you can get em and piles of trees if u can cut em. small pine trees offer no cover no matter how many prickly branches you stack, heh. thought i was safe behind the 4 feet of pine tree branches but nope, paintballs cut through like a knife through butter and hit me hard.

pretty much any junk you can find that can withstand a paintball can be stacked to make a bunker.

if your playing in dense woods cut all the branches off trees.

make A LOT of bunkers, even if you think you have enough, you dont. more bunkers the better.