Chain-link fences and even barbed-wire fences often have tension wires running diagonally across a fence panel and attaching to two corners of the panel. These tension wires are used to keep the fence taut and prevent it from sagging and bowing in or out. If the tension wires on your fence have become loose, you'll need to tighten them as quickly as possible to avoid permanent damage.
Locate the top tension clip, which is located on the top portion of the wire on the fence panel. You should see a small clip holding the tension wire in place. This clip should have nuts or screws that control the tension.
Tighten the top clip, using pliers or a screwdriver to turn the nuts or screws clockwise. Work slowly, going a quarter turn at a time. You should notice the wire beginning to tighten. It may even sound like a guitar string as it tightens.
Tighten the bottom tension clip. On the opposite side of the fence panel, at the bottom, you should find another tension clip. Adjust this clip just like you did the top one, turning the nuts or screws clockwise a quarter turn at a time. Tighten until the fence doesn't sway, sag or bow. You shouldn't be able to move the centre of the wire more than a quarter inch in any direction.
Repeat the process with your other fence panels. If one tension wire was slack, chances are the others may have loosened as well. Go to each panel and repeat steps 1 through 3 until the entire fence has been tightened. Keep in mind you may need to do this annually, particularly if the area gets a lot of snow that drifts onto the fence, making it sag.