I've tried water, dog food, sand, gravel, metal weights. I settled on sand bags. I buy play sand, empty the bag to about 30 lbs, duct tape the heck out of the bag. I then fill 1 gallon ziplock bags with sand, tape the heck out of them. You need to completely duct tape the plastic bags or they will wear and leak. The 1 gal bag will be 5-6-7 lbs each. I use the 30lber as the base, then add 5-6-7 lbers after that. I put a cheap sleeping in the bottom to lift the weight off the bottom, sand bags on top. That system works well. I normally start with 35 lbs about now and work up to 75 lbs by October. I start with 3 miles, flattish terrain, build to adding terrain to reach 75 lbs and 6 miles. And about August it starts to suck <G>
