Want to lodge in tower? Up to a certain point (4-4)
I believe the answer is:
knee-deep
'up to a certain point' is the definition.
(up to one's knees)
'want to lodge in tower?' is the wordplay.
'want' becomes 'need' (synonyms).
'to lodge in' indicates putting letters inside.
'tower?' becomes 'keep' (I've seen this before).
'need' going inside 'keep' is 'KNEE-DEEP'.
(Other definitions for knee-deep that I've seen before include "Heavily involved - up to leg joints?" , "Immersed up to the patella" , "Coming half way up the leg" , "Deeply involved (in something)" , "Submerged to one's patella" .)