Do you want netting or some strands of electric? Netting is pretty high maintenance but more effective. A couple or 3 strands of polywire / tape will keep foxy away most times.
If you go the polywire route you will need some polywire (doh). You will need some posts. You can get those plastic posts with a spike which are easy to push in and move but you may want some timber posts on the corners or turn points and if so, you will need isolators to stop the wire shorting on the wood.
Once you have your strands set up (or net if you like strimming), you need an energiser. This can be a combined unit with disposable battery built in or you can get seperate energisers which run off a mains connection or a 6 or 12v leisure battery which will need occasional recharging. You hook the battery up to the energiser and the energiser to the fence and an earth stake (long metal stake which you whack into the ground).
Then you are good to go.
Have a look at the Hotline website. They have some good pages with suggested set ups for various uses.