Hey guys, I have a customer who has a basement home. He has a brick retainer wall going from the basement around to the front and ends about 12 ft from his sidewalk. He has areas on each side he wants to landscape and cover with river gravel. I plan to use the Windsor stones beginning where his wall ends and make 2 rows on each side of the walkway. My question is how high do I need to go to keep the gravel from washing down in a heavy rain. I know without seeing it is a stupid question. I thought there might be a rule of thumb as to the degree of slope you can work with. My guess is it is a 35 to 40 degree slope now. I haven't made pics yet as I just got the call a while ago. Thanks in advance. Oh,if you have any ideas for heat loving plants I'm all ears.