Marty is right, you can restretch and re-attach. DO USE hot wire on the inside. What a wonderful assist that is.
Yep, if it isn't too bad, you can kink it and it will tighten. I use a hammer. Put the claw end onto the wire, like you would if pulling a nail, hold the head of the hammer with one hand and the handle with the other, then twist it..........
OK.......hold hammer in front of you, left hand on head of it and right hand on handle, horizontal to ground. Now push hammer forward so that the claw has a piece of horizontal wire within the claw. Sharply twist the hammer up with the right hand and down with the left. You have just made a "z" kink in the fence. Do this this from top to bottom in that row and you have started to tighten the fence...I've had to do this in a couple of row within a section of fence between posts to get it back in line but, it works great.
Another reason for hot wire besides keeping butts off, it keeps the stallions from trying to climb onto the back of another in the adjacent field. Getting hung up in this fence can be major, major problem.
Then build them a section of fence within the pasture that they CAN be allowed to rub on
It's a fact that the minis "must" rub
I find that the four posts I put in the ground to fence off a couple young trees has been a real jewel for this. They love it. This winter I plan to replace the fence with some newer, it's getting a lot of wear!