i put gravel at the bottom of the pond vs the lava rock only because i was able to source it for free. lava rock is much more porous for more bacteria growth. but like i said i had about a ton of this stuff for free so that is the way i went. and from what i read about depth, around 3 feet will suffice but you will still will need the de-icer. the de-icer is just a plastic heater that keeps the water around it 34+ degrees i have also read about placing an air stone to keep the water agitated. as far as keeping it clean ocasional water cheanges are a good idea other than that depending on your water volume the pond should do a pretty good job of keeping itself celan. make sure you use lots of plants and not a lot of fish.