I tend to do a lot of SFG, but I have one bed that I like to reconfigure between 1 foot squares and 2 foot squares (pumpkins, etc) depending on the season. So I put together a kit that lets me use 20mm electrical conduit (DETA from Bunnings if you're curious) as my divider, clipping them in and out and resizing my squares as required.
You don't need to resize the squares if you prefer, it will sit quite nicely in a static configuration.
The pictures above are of the system that's actually already been in place for over a year, including two Australian (melbourne) summers - so it definitely holds up! Can't verify for places that get snow levels of cold, but it definitely survives the fires of hell.
Attach the end clips to the inside of your growing bed, lining the centre of the clip with the 1 foot mark on all four sides. (I did this at one foot intervals on my 13 foot bed). Cut your conduit down to size and clip into place (mine is a 2 foot by 13 foot bed, so I cut 13 2 foot pieces and then clipped the 1 foot pieces in between). To resize, simply pull the piping out of the mounting clips and put somewhere safe while you use your expanded squares.
There are two versions of the four way connectors - one allow you to slide it over your vertical struts, then clip the horizontal ones in and out as required, the other allows you clip on all four angles. Both hold up rather well, so I think it's down to personal preference. That said, I'd probably recommend the slide/clip for longer runs, or when you need something a bit more robust.
I did actually make a version with all four sections solid, but found it an absolute pain to try and add/remove the 1 foot pieces the further you went along the bed which is why they're clippy.