A lawn joke is:
 
“I have a chicken-proof lawn. It’s impeccable.
 
English writer and comedian Tim Vine told the joke in 2012.
  .
         
Wikipedia: Tim Vine
Timothy Mark “Tim” Vine (born 4 March 1967) is an English writer, actor, comedian and presenter, known for his quick-fire puns and his role on the BBC series Not Going Out until his departure in 2012. He has released a number of DVDs of his stand-up comedy and has written several joke books. In 2010 and 2014, Vine won the award for best joke at the Edinburgh Fringe Festival. His winning jokes were: “I’ve just been on a once-in-a-lifetime holiday. I’ll tell you what, never again” and “I decided to sell my Hoover ... well it was just collecting dust.” He was the runner up in 2011, 2012 and 2013.
 
Shropshire (UK) Star   
Review - Tim Vine’s Chat Show, Oakengates Theatre
Telford | News | Published: Oct 2, 2012
The world’s fastest joke-teller hit the ground running in Telford last night with a barrage of one-liners that had the sell-out audience in stitches from the start.
 
“I’ve got a new chicken-proof lawn . . . it’s impeccable. My chicken lost her eggs . . . she’s probably just mislaid them.”
     
12 October 2012, Great Yarmouth (UK) Mercury, “Volley of gags hit their targets”:
The Tim Vine Chat Show
Drill Hall
Great Yarmouth
(...)
Like the church pastor from Lowestoft stuck in drainpipe jeans in a changing room, he had to manoeuvre from some tight spots but in the end the show - like his chicken proof lawn - was impeccable.
 
Twitter
John Archer‏
@TheArchini
Replying to @GaryDelaney
@GaryDelaney “I’ve got a chicken proof lawn, impeccable!” - Tim Vine 😉
4:42 AM - 21 Oct 2012
 
Twitter
Roy Manterfield‏
@MumblingNerd
I’ve made my lawn chicken-proof; it’s impeccable.
12:19 PM - 23 Oct 2012 from Nottingham, England
 
Twitter
Sam‏
@SamMatthews96
I’ve got a chicken proof lawn - It’s imPeckable
3:23 PM - 4 Dec 2012
 
Reddit—Jokes
I’ve got a chicken proof lawn
submitted December 20, 2015 by Iamabioticgod
It’s impeccable
 
Twitter
Shit Jokes‏
@ShitJokes
I’ve got a chicken proof lawn.
It’s impeccable.
3:21 PM - 28 Jun 2016
   
Reddit—Dad Jokes
I have a chicken proof lawn… (self.dadjokes)
submitted June 29, 2017 by madazzahatter
Its impeccable…
 
Reddit—Jokes
I have a chicken proof lawn…
submitted June 30, 2017 by madazzahatter
It’s impeccable…
 
Reddit—Oneliners
I have a chicken proof lawn…it’s impeccable.
submitted October 6, 2017 by madazzahatter