He lacks power to go over one's head but does (6,5)

'head but does' is the definition.
I know nothing about this answer so I can't tell whether this works.

'he lacks power to go over one's' is the wordplay.
I cannot really understand how this works, but
'he' could be 'der' and 'der' is located in the answer.
'power' could be 'p' (symbol in physics) and 'p' is present in the answer.
'over' could be 'o' (cricket abbreviation) and 'o' is present in the answer.
'one' could be 'li' (I've seen this in other clues) and 'li' is found within the answer.
The remaining letters 'gilt' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?