I used these 1"wood screws they had at HD with little rubber washers made for roofing material, the plastic you see on mine is stiff polyvinal roofing material, 3ml plastic may rip in the wind so i would use fir stripping and wood screws, so you get a good ammount of surface covered where it attaches, and it will be less likely to rip. We thought about plastic but were worried 3mm wasnt thick enough and couldnt find 6-7mm in clear. It was $80 with a coupon for the roofing stuff, but i was able to cover my run 36" high all around, and hopefully it will last a couple years. The rolls of plastic were like $45 or so, not counting the fir stripping or lattice we were going to buy to hold it down. I also liked the idea of being able to easily attach and detach the panels with a few screws, so when the weather is nice we can open things up, or close in badRhoise, how did you connect the plastic to the outside of the pen? I've got my 3mil plastic and was thinking about using duck tape. (I've got quite a bit of duck tape and it seems to work well on many projects.)