The most common and most likely answer to this crossword clue is the 7 letter word MUDFLAP
I've seen this crossword clue in The Daily Telegraph
M
U
D
F
L
A
P
Buddy explains!
The straight part
We know that "one should protect against dirt on an estate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one should protect against dirt on an estate = mudflap.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 MUDFLAP mean?
MUDFLAP noun- A rectangular flap mounted near the wheel of a truck to prevent mud from being thrown up onto the vehicle.