I've been playing Fantasy Flight's Relic lately and really love the character pawns it uses. So I boiled up some Instant Mold and made a quick casting of the Ultramarine pawn. This was stuck to a base and Celluclay used to fill in around it. Then sand, "rubble rock", and a couple of Imperial Guard bits. Rubble rock is Durham's Rock Hard Water Putty that I put in a coffee grinder and then sieve into various grades. It looks a lot like exploded brick rubble and works well for urban themed bases.