Followed loch, showing persistence (10)
I believe the answer is:
doggedness
'persistence' is the definition.
(I know that persistence can be written as doggedness)
'followed loch' is the wordplay.
'followed' becomes 'dogged' (I've seen this before).
'loch' becomes 'ness' (Loch Ness in Scotland).
'dogged'+'ness'='DOGGEDNESS'
'showing' is the link.
(Other definitions for doggedness that I've seen before include "Persistence" , "Tenacity" , "Determination" .)