You do not want to use grave/crushed rock as your backfill after a termite treatment. Termidor does not bond to rock, it bonds to soil, so if you fill in the trench with gravel, the termidor will not stick to it and it will leave you with a 6x6 area of completely unprotected surface that the termites could pass through to get directly to your home.
This Vigoro cu. ft. Black Lava Rock can be used to accent your garden or planters. It can be used for landscaping around trees, shrubs, decks, driveways and other areas. The natural, crushed lava rock resists fading and cracking and won't attract wood pests, such as termites and ants.