Roto Rand
\_\_ \\_\_\_\_\_\_\_\_\_/
EdgeDetect\_\_/
\_\_\_\_\\_\_\_\_\_\_/
\_\_\_\_\_outside
(ignore the underscores, had to add them to get spaces)
Scale, blur, etc... the Rand. Also try replacing the Rand with a checker and bluring/rotating that. Then add/subtract it from the original roto. Layer a bunch of this stuff like this to get a nicer randomness. There are a bunch of different generator macros.