Since I have secured the yard fence, I can freely move the pens around the area without fear of intruders other than the flying kind. I do cover the pen with 2 inch plastic net to keep the owls out. I n the absence of a protected perimeter fence some provision will be needed to keep out the climbing intruders. An electric fence can be placed near the top of the moveable pen. Always place electric fence wires high enough that the birds cannot touch them.
Electric fences scare off the predators, but they often kill birds.
Do not under any circumstance substitute a cheaper quality pipe for the Schedule 40. You need the wall thickness of the Schedule 40. Connect and glue three pieces together, then repeat the gluing for the remaining three pieces. After each gluing, be sure to wipe off the extra glue, as it will weaken the joint if it pools. Then let the glue dry for about an hour.