That's why I make sure to recommend 1x2 or 1x1. 1x2 mostly. 2x4 is fence wireI made the mistake of making our enclosed run out of 4”x2” galvanized welded wire. It worked fine for a few years until rats discovered the run. We have now had to completely enclose the welded wire with 1/2” hardware cloth because the 2” openings are big enough for rats to squeeze through, also squirrels. I wish we had used the hardware cloth to begin with. It would have saved us lots of time, energy, and $$$.