If the base of your panels are attached with 3/4" staples, replace them with 2" fence staples. Our chickens can push out 1 1/4" & 1 1/2" staples and we had to go with 2" ones. Predators can definitely pop them out - especially if attached on the outside of the base - LOTS of pressure on those tiny/short staples - not enough length to hold the cattle panel to the board base. How did you get the 3/4" staple to "fit" around the cattle panel? Also, the panels would need to be attached at every square (20 staples - at the top arch) and possibly more. Similar to the way you did the bottom (that I can see).
To go with the idea suggested by Gary. If you go with the arch, then pull the ends together & overlap by one or two (stronger) full squares and wire it together first (one continuous wrap from one end to the other) on both sides, then attach your ridge pole centered between the overlapped edges. I would use counter sunk u-bolts to attach the "doubled"(overlapped) panels to your "ridgepole" - at least 4 & possibly more. Pulling the ends together and overlapping them will lower the finished height of your project, but you will gain back the stability that you need to support whatever you use for your roofing. There will still be a tremendous amount of pressure on the two "sides" or ends that are wired together - that's why I recommend wrapping it with wire (or sturdy rope). This should work and hold up well for you.
Or instead of an arch, you could wire top panels together in an "A" frame. You will gain the strength back that you lost by using the short panels and trying for an arch that has lost it's support. The two panels butting together will be strong. You can also still use a ridge pole, too. If you do, you will still need to attach it with something stronger than 3/4" staples every 3'.
What are you building on the open end where the cattle panel doesn't go all the way to the end of the base unit? I'm figuring that's where you are putting a wall and nesting boxes?
You are on the right track, don't give up. Our "temporary" hooped coops, meant to be movable tractors, have turned into permanent housing for 3 different sets of hens/roosters and have survived two full moves on pickup truck beds not fully supported on both sides, high winds and driving rains (+ hurricane Matthew) and ice storms here in NC. The oldest one was finished in Sept 2014 and the newest in November 2014. So the oldest is a little more than 2 1/2 yrs old. It was also "tractored around" on our first property where it was built and again when we finally moved into this property.
We plan on building more hoop coops - as permanent structures. We LIKE them!!! We even use them in conjunction with pallets to make "sheds".
To see how we set up the first one and the build and a couple of pics of the temp shed when we moved the ponies off the leased property to rented space while we closed on our permanent property - go here -
Maintenance and Pony work