Recently, Clyde and a calf have been wandering outside of the fence. Farmer John and I spent a couple cold afternoons fixing the places they were getting through.
In places where all the strands of barbed wire are intact, we put in "fence-stays", which are the metal twisty things pictured below. They are placed in between two fence posts and twist down over four strands of wire. Fence-stays hold the wires together so that when a cow tries to push through the fence they end up pushing on all four strands - this makes the fence much stronger. They are very easy to install and we hope this will help prevent so much cavorting in the front yard.
There were several stretches where someone (probably Clyde) broke the barbed wire. In those spots Farmer John ran new strands of wire.
I would hold the wire tight with the fence pliers.