I'm building a Unilock patio for my parents around the new pool that was just installed. on the far side of the pool there used to be a deck, so the grade is a little low. Now there will just be a walk around that side of the pool and there is going to be a considerable drop in grade. Max height is about 16-18" while the lowest will be around 6". We're looking at the unilock retaining wall material, but it quickly add's up in cost (which isn't a problem) but they don't want to spend big bucks on that side of the pool where no one will ever see it. So, is there a low budget material i can use other than plain old rock and building one with mortar?