Spell lockFollow

I use a /focus pair of macros. The first sets the focus, the second uses the [target=focus] modifier for all pet abilities that require targets. WowWiki has tons of examples, esp on the warlock macros page.

... or you could look in the Allakhazam wiki: http://wow.allakhazam.com/wiki/Warlock_Macros_%28WoW%29

I find the easiest way to spell lock your pet's current target is to set spell lock to "manual" mode, meaning that you actually have to click when you want your pet to spell lock. Then send your pet to attack your target, and when you want him to spell lock, right-click the spell lock button. This will cause spell lock to turn back to "automatic" mode, and in that mode the felhunter spell locks instantly (every 30 seconds). After right-clicking, right-click again to set it back to manual mode. The whole process sounds really complicated but you're really just spamming the right-click button twice.