Rabbit Scenting under chin

Hey,
I have noticed that smudge has a discoloured patch under his chin, I assume this is from scenting, but I am finding it difficult to clean (or get to) as he is a ****** to hold, anyone have any tips, I do have some gromming wipes, but it looks like it needs a brush aswell HELP...
x

Is it wet or anything? If he were dribbling it could indicate dental problems?

No it's not wet, it's like a dried browny colour, I have read somewhere before, that males can scent alot and the hair under the chin can get matted.