What are you planting it in? Screw into the bottom of the trunk!
Take a look at my privet air layer thread, I screwed a small plank of wood to the flat bottom, then screwed into the plank via the tie down holes:
Disclaimer: this was my first air layer, and I had to remove early because the neighbor called in the hedge trimmer man (who am I to say anything, they're paying for it). If it survives, I'll document progress here. No idea where I want to take it; I'll have to stare at it awhile now that it's...
www.bonsainut.com
I still anchored it with a couple wires over some branches and around the bottom of the pot just in case.