Excellent tip, and a great project description! I always have a good laugh when I see the pitiful tomato cages offered for sale in nurseries.
A T-post driver is cheap, simple, and an almost indispensible tool for any serious gardener.
For those who may not be aware, the wire in these cattle panels is 4 gauge (.2043") which is just the thing for supporting a thriving stand of tomato vines.