Hello James,
I have kept various kinds or types of Anubias in my tank, and onething I have learn is you NEVER burried the Rhizome, the roots can be burried in the gravel, however that is the only part of these plants which you to burried. The majority of them are slow growing, they can however grow a little faster if you fertilize your tank regularly, and provide addequate CO2 levels.
Sincerely,
Aquario72.