The most common and most likely answer to this crossword clue is the 15 letter word NO-HOLDS-BARRED
I've seen this crossword clue in The Times
N
O
-
H
O
L
D
S
-
B
A
R
R
E
D
More clues leading to the result NO-HOLDS-BARRED
Buddy explains!
The straight part
We know that "Fully open/as any lock can be picked" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fully open/as any lock can be picked = no-holds-barred.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.