Did you guys get a survey before you did them? Or did you leave space to make sure you were covered.
I had a guy come with a metal detector and found the pins in the front yard. I also had the a copy of property map in our possesion and also looked it up on Beacon. I used the measurements off the maps to determine the layout lines. I then strung both property lines and put my corner post where the two lines crossed. You never know when Pythagorean theorem might come in handy. I used that it and low and below everything was square. My biggest issue was the corner post as it was about 2' from a utility pole and I had be careful of the marked underground power lines and buried cable lines. Once I started digging I came upon a 6" tree root from the neighbors tree they had taken down about 5 years prior. Thankfully it had decayed enough to get through it without a lot of issue. I even moved one neighbors chain link fence post close a gap. He was thrilled that I did it as he had wanted to but never got around to it. So it was a win/win for both of us.
If you do three things when you are going to put up a fence these would be the three things:
1. Talk with your neighbors about it first. It makes things so much easier.
2. Always call before you dig. I got all my electrical, cable, and gas marked out in a couple of days!!
3. Get a post level. This took the guess work out of making sure the post were level in all directions.