Our flagstone was installed last June, so it's coming up on 1yr. We also have a SWG system. The 'type' of flagstone we have is an "Oklahoma Wister". It is not flaky, but it does tend to generate sand and has really obtained a weathered look to it. There are a few locations that have some pitting, where others have actually worn in a very smooth pattern. Something that our builder/contractor did was to bevel the bottom corner near the water, so there is not a sharp edge to hit your head on.

KT