For anyone who doesn't know of this kind of fencing here is a link: Ready to Install Kits
Scroll down a bit and you'll see what it looks like set up. I only use 3 strands. For younger horses I'd recommend at least 4. It comes in green, brown, or white (I use white for high visibility) and can be used with basically any kind of post - T-posts included. They also sell these cool little lights to clip on the fence so they can see the boundaries in the dark very well. I haven't gotten any yet, but plan to when I get home.
It can get kind of pricey for larger areas, but for smaller pastures it's not too bad. I even made a round pen out of my extra tape and didn't electrify it and my horses did just fine with it. Like twogeldings uses, there are different kinds - I am not sure if they are cheaper or more expensive, all I have used is this kind.
Let us know how your boy does :)