Easy Diy Cross Country Jumps . Other ways that you can build cross country fences is to use your show jumps, but use natural poles rather than painted ones, and add fillers such as: Measure every 20 in (51 cm) down 2 treated 1 in × 4 in (2.5 cm × 10.2 cm) planks. Fast....easy...recylced...homemade cross country jumps (pics) Cross from www.pinterest.com Prop them up with wing standards and add trimmings from trees. This will give us a very stable. So for this example, our feet for our 4 ft standards will be 20” long.