So pretty much, we screwed up. Even though we measured over and over again, when we had actually finished concreting in the gate posts for our gate, the gate posts were too far apart. So, we had to figure out how to build one custom gate.
First we had to build the frame. We did this by purchasing top rails. Ours were 1 3/8 inch in diameter. We measured very carefully, and cut them to size. Below is a diagram displaying how we calculated how long our rail segments had to be. We needed our gate to be 51" in width. By testing the elbow pieces and seeing how far we could shove the elbow pieces onto the rails, we calculated that because the elbow pieces added 2 inches onto the length, our segment needed to be four inches shorter than our 51" width. Follow the same procedure for the gate length, and keep in mind the total high should be about one inch shorter than your fence height, so the gate is able to swing without touching the ground. Ours measured 47" tall for a 48" fence.
Here's a close up of the gate elbow.
Then we used gate hardware to put the gate in place.
We proceeded to attach the fencing to one end of the gate using 1 3/8" tension bands, stretch it to the other, and attach at that end.
And we have a gate! We still need to trim the top off of the chain link fencing, but for now that's just a cosmetic consideration. Our puppy can now run around!