Problems filling hole up where land slopes (8)
I believe the answer is:
hillside
'land slopes' is the definition.
(sloped area of land)
'problems filling hole up' is the wordplay.
'problems' becomes 'ills' (I've seen this in another clue).
'filling' means one lot of letters goes inside another.
'hole up' becomes 'hide' (to hole up somewhere is to hide there).
'ills' going inside 'hide' is 'HILLSIDE'.
'where' acts as a link.
(Other definitions for hillside that I've seen before include "Where Arnold's Scholar travelled" , "The slope of rising land" , "Incline" , "Slope of a small mountain" , "Where climbers may start" .)