Place a sheet of paper underneath each of the windmill's feet as it rests on a flat, hard surface. Cut around each foot with a razor knife so you have an opening in the paper the size of each foot.
Place the windmill, with the papers around the feet, in the exact spot you want it to stay.
Pin the papers to the ground with three tent stakes per sheet, then lift off the windmill and set it aside.
Inspect your windmill's feet. If you they have holes in the bottoms, choose four pieces of rebar or all-thread tubing that will fit inside the hole. If holes aren't present, drill your own using a drill bit slightly bigger than the diameter of your rebar or all-thread pipe. If your windmill has loops that sit outside the feet, use all-thread that will fit inside these loops and adjust your paper holes to line up with the loops instead of the feet.
Drive your rebar or all-thread pipe into the ground. Pound in rebar with a hammer until about 2 inches (or the depth of your windmill feet holes) show above ground. For all-thread pipe, twist a nut onto the threads so it rests just above the top thread, then pound the pipes into the ground with a rawhide or rubber mallet, using the nut as a nailhead to protect the threads. Move the nut to each pipe as you pound it in and discard the nut when you finish.
Mix two-part metal epoxy according to the package directions. Spread a generous amount on the top end of each rebar or all-thread piece, unless your windmill has loops instead of feet. Place the windmill feet over the epoxied metal and hold it in place while it sets.
Place your windmill base loops over the all-thread if you are using these instead of holes. Place a fender-style washer over each piece of all-thread so it covers the metal loop. (Fender washers are much broader than standard washers.) Tighten the windmill in place with nuts over the washers, using a wrench to ensure a snug fit. Tighten metal or plastic threaded caps over the threaded pipe ends to avoid injury from the exposed ends.