The most common and most likely answer to this crossword clue is the 9 letter word DESIGNING
I've seen this crossword clue in The Daily Telegraph
D
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S
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G
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More clues leading to the result DESIGNING
Buddy explains!

The straight part
We know that "planning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case planning = designing.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.
What does DESIGNING mean?
DESIGNING verb- To plan and carry out (a picture, work of art, construction etc.).
- To plan (to do something).
- To assign, appoint (something to someone); to designate.
- To mark out and exhibit; to designate; to indicate; to show; to point out; to appoint.
- To manifest requirements to be satisfied by an object or process for them to solve a problem.
- A process of design.
- Artful; scheming