Ah, gotcha. Sand bags, as per punisher's suggestion, will likely be the best option, in the interest of keeping cost of materials and "harvesting" to a minimum, while having the lowest impact on the surrounding environment. Used tires may be a viable option, but require work so they don't hold water and become breeding grounds for all sorts of nasty stuff.
Things I would like to purchase with American dollars:
1: Scorpion marker (the old spyder clone)
2: A nice unmolested Nelspot 007 pump handle
3: A noxx or jcs bottomline stock
4: Hammer 7 thumbwheels