Hi Matt - water flow in/under/around rocks are always an issue - and personally I found that this is one of the main reasons for problems in our tanks. As detritus settles EVERYWHERE in/under/around rocks and causes leaching of everything bad, but mostly phosphates (which is the main fuel for nuisance algae).
Ideally you want to have a power-head or two underneath your rockwork (even the cheapest powerheads) just to ensure that there is really decent water-flow in/under/around your rock-work....
The problem I found, is that with MOST aquascaping designs - IF you do not have the power-heads at the right places, you will still end up with detritus somewhere that might cause problems in future.....
I personally think that one should go back to having multiple small power-heads hidden away, rather that trying to have the correct water-flow with only one or two minimal power-heads/pumps....
My next re-design in my aquascaping will definitely include more water-flow in/under/around my rock-work....
Irie Ivan for example has about 5 or 6 power-heads hidden away behind his rock-work, and these are purely to keep detritus from hiding away - not for water flow in his tank....