If you have access to logging chains, or cable, set trailer tie down screws off each end. Tighten the cable or chain to pull the fence in line or tight again. Then put in your corner braces. If the fence is still a little loose then use linemen pliers to put evenly spaced crimps in between welds and this will tighten the fence. Be careful because welded wire is a light gauge, too tight will pop welds and the wire itself.
You can find the tie down screws at Lowe's or Home depot. If your ground is solid you may be able to get away with using pet tie out screw stakes.
You can find the tie down screws at Lowe's or Home depot. If your ground is solid you may be able to get away with using pet tie out screw stakes.