I would be leery of doing the hole on the underside just for the problem of trying to get them lined up exactly in the same spot next year. I am struggling with the same issue right now with some PVC window frames. Currently I hang the pvc on 2 hooks at the top of the window. But now I am trying to use the Boscoyo corostrips to get real nice alignment on my lights. The hooks can't wrap around the pvc anymore because of the coro and end up twisting the corotrim from front alignment to up to the top. I've thought about using the drill the holes technique, but I have 4 identical window frames and currently I can hang any frame on any window, But when I originally put the hooks up I just eyeballed their placement and so if I drill holes I will always have to put the same frame on the same window every time. Compounding that I have hooks in place for storing those frames off season and they would not match the drilled holes either. I can certainly go back and put new hooks in place using a standard placement, but am pondering while I try to come up with a better way.
Long story about my problem, but I would anticipate the same issue with the yard borders. Not undoable, but more work than I like to have when it comes to setup time and for me storage also. I would probably just put a zip tie around the rebar and the pvc. Just my 2 cents.