A group of Mounties plan a demanding walk (9)
I believe the answer is:
esplanade
'walk' is the definition.
(I know that esplanade is a type of walk)
'a group of mounties plan a demanding' is the wordplay.
'a group of' says the answer is hidden in the clue (group of letters from the clue).
'ESPLANADE' is hidden within 'mounties plan a demanding'.
(Other definitions for esplanade that I've seen before include "walk by sea" , "Walkway along the seashore" , "A leap ends (anag) - seaside feature" , "Seaside road" , "Paved area at seaside resort" .)