I take 2"x2"x1/4" angle iron, cut short pieces into points, one piece is a single point, the next a double, I then take a length of the angle iron, weld those pointed pieces on, also drill or cut a hole for a landscape spike on each side. Once the points are welded on, I sharpen them with a grinder, finish with a file. It rusts up in no time, old rusty steel is even better. I then take the piece, place it where it is easily hidden, then drive 2 landscape spikes or whatever to pin it down, drive over that, it aint no boards with nails to bend over that is for sure.
I absolutely do not like having to put these out, they're still at the last location they were passing through, which is closed up and covered up with prickers, I have yet to move them again, leaning towards doing that now, honestly wish people would get the idea here.