Person sliding down rocked boat, going over stone (11)

I believe the answer is:

tobogganist

'person sliding down' is the definition.
(tobogganists slide down slopes)

'rocked boat going over stone' is the wordplay.
'rocked' is an anagram indicator.
'over' means one lot of letters go next to another.
'stone' becomes 'st'.
'boat'+'going'='boatgoing'
'boatgoing' with letters rearranged gives 'toboggani'.
'toboggani'+'st'='TOBOGGANIST'

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.