how to keep all 4 sides equal dist. and square. This is for a pond.?

Question

I'm having trouble getting my 650 ft 4 sides equal.

Answer 1

Each side = 162 1/2

Answer 2

Once you get it roughed out and approximately the way you want - re-measure the sides to assure they are all equal in length and then carefully measure the distance of the diagonals - the distance across the opposite corners.
These two distances should be exactly equal if the corners are 90 degrees. If not, you can move either end over slightly until these measurements are the same.
Once everything checks out - you've mastered it.