A popular lawyer joke (among many) is:
 
Q: Why should lawyers be buried 20 feet underground?
A: Because deep down, they’re good fellows.
 
The joke has been cited in print since at least 1990.
 
 
18 February 1990, Augusta (GA) Chronicle, “Scholar swears by work (Dayton Daily News), pg. 2D, col. 1:
Q—Why should lawyers be buried 20 feet underground?
A—Because deep down, they’re good fellows.
 
23 December 1990, The Orange County Register (Santa Ana, CA), “Oregon is rolling out star QBs” by John Hall, pg. D19, col. 1:
KMPC’s Robert W. Morgan had one that works for either lawyers or sports writers. “Why do you bury sports writers 15 feet deep when they die?” Sure enough, “because deep down they’re really not such bad guys.”
     
Google Books
Great Lawyer Stories:
From Courthouse to Jailhouse, Tall Tales, Jokes, and Anecdotes
By Bill Adler
New York, NY: Carol Pub. Group
1992
Pg. 129:
You know why they bury lawyers in graves dug twelve feet deep?
‘Cause they heard that deep down, lawyers are good people.
 
Google Books
Country Chuckles, Cracks & Knee Slappers
By Michael Lessiter
Brookfield, WI: Lessiter Publications
1992
Pg. 223:
Do you know why attorneys are buried 20 feet under the ground? Because deep down, you know there has to be some good in them.
 
Google Groups: rec.humor
Lawyer Jokes
Mahesh Ursekar
9/18/92
(...)
—23—
Q:  Why should dead lawyers be buried 16 feet deep?
A:  Because deep down, they’re real nice people.
 
Google Groups: rec.humor
Lawyer Jokes
david engel
6/9/94
(...)
26.  Q.  Why are lawyers buried 12 feet underground?
A.  Deep down their good.
 
Google Groups: rec.boats
Rec.Boats vs Rec.Boats.Cruising
William R. Williams
7/13/95
(...)
Q. Why should lawyers be buried 100 feet under the sea?
A. Because deep down, they’re really good people.
 
Google Groups: aus.jokes
Lawyer jokes
Hyatt Saikin
3/20/96
(...)
When lawyers die, why are they buried in a hole 24 feet deep?
Because deep down, they are all nice guys!
 
Google Books
Primary Justice:
A Novel of Suspense
By William Bernhardt
New York, NY: Random House
1997
Pg. 288:
“Know why lawyers are always buried at least twelve feet underground?”
 
“Forget it. That’s not why I came.”
 
“Because deep down, they’re really nice people,” Tidwell growled, obviously disappointed.
 
Google Books
The Mammoth Book of Humor
By Geoff Tibballs
New York, NY: Carroll & Graf
2000
Pg. 185:
When lawyers die, why are they buried in holes 20 feet deep? - Because deep down, they’re all nice guys.