I agree that ramming your boat into/over submerged rocks will only serve to weaken your boof. The best boofs out there are the ones where you don't actually hit any rock at all; it's just you, the water, and then some air!
If you practice these steps below, you should be boofing your creek boat way better than that little play boat in no time.
#1: look where you want to boof and line up for it. Spot your take off point and make sure to get yourself there. Again, you are NOT looking to go careening off rocks--that ain't boofing, that's just plain lame ol' rock bashing.
Check out this photo:
In a boof situation like this, you want to line up as close to the rock creating the boof as you possibly can without actually touching it. This is the place you will have the most speed, be able to get the best paddle stoke in and seperate your boat from the water with the most ease. Hitting the rock will only slow you down.
#2: Time your strokes. You often see people frantically paddling to the lip of a boof--forget that. Slow and calculated strokes are what you want. Make sure you time it so that your last stroke is right at the lip of the boof, even grabbing water that is already falling of the edge. Timing is everything!
#3: make sure that boof stroke is a good one. Get your paddle as vertical as you possibly can, remember you want to propel yourself up and forward. So the more vertical your paddle is the more this will happen (you don't want a sweep stroke here). Plant the blade up between your knees and your toes, and pull back, straight along the boat until the blade is about at your butt.
#4: as you take that boof stroke, pull up on your knees and thrust your hips forward (Note: do NOT lean back! Maintain an upright body position with your torso, just pull up on the knees, thrust forward with the hips). This action, combined with the well-timed paddle stroke should disengage your kayak from the water, sending you airborne into your "boof."
#5: upon landing, you will be sitting in an upright and ready to paddle position if you've properly done step #4. So you want to land, and immediately paddle out of the backwash of whatever it is you've just boofed over.
Say you've just taken a left boof stroke (like in the photo), well then you should be ready upon landing to immediately take a right stroke to get going downstream.
Like someone already said, you can practice this by boofing over small holes in the river. You don't need the perfect boof to practice on. Anytime you see a little hole, practice steps 1 through 5 and boof over em. It's the exact same feeling as boof in the photo, just less dramatic.
I hope this helps.
Let me know if you have any questions.
Small World Adventures