For the construction of a military obstacle course you will need to make a trip to the junk yard. There you can find some of the necessary materials to complete your project. Tires are a necessity, of course, and used tires can be found easily at almost any junk yard. You may be able to locate large pieces of pipe, as well. This pipe can be used to form tunnels for crawling through. You can make balance beams as well, and add ropes and nets to climb. If possible, bare walls to climb will be an excellent addition to the project. Ladders can be used also and mud pits are another good addition.