After UH Plant Ops removed the defunct swamp coolers in front of the greenhouse, it left two large holes in the greenhouse where the coolers once connected. Until recently, I simply covered the holes with pool wrap (the blue bubblewrap-like material), but I noticed that cats (and probably other small animals) were able to enter and exit from the holes despite the covering.
So, in preparation of our gro pods and to stop this problem, I filled and plugged the holes. First, I added in four cinderblocks (18''x6''x6'' each) into each hole, stacked 2x2 blocks.
Then, I put PVC pipe through one of the cinderblocks and ran a hose through the PVC.
To fill the hole, I used big gap expanding foam sealant. I had to go back to Home Depot to purchase a second can because one wasn't enough. Of course, use adequate protection, since the foam is sticky and irritating.
Once all the big gaps were sealed, I added steel wool (#12) into the holes of the cinderblocks to prevent any rodents or pests from getting through. I decided to leave the pool wrap on, since it looks better than the yellow foam sealant.