What about Paul Drake?

I am reading the Erle S. Gardner Perry Mason books in order of publication. No particular reason except that I have the books, the time and the inclination. I am always happy when I get some background information on Perry, Della and Paul. A bit about Della's family life is discussed in the first book, The Clue of the Velvet Claw.

Paul Drake, Perry Mason's favorite investigator, is such a dish as portrayed by William Hopper on the TV show. And a heavy smoker. From Book 2, The Case of the Sulky Girl.
Paul Drake perched on the edge of Perry Mason's desk and shook tobacco from a cloth sack into a brown paper which he held expertly between cigarette-stained fingers.
(Pocket Book, 1962, p. 186)
Paul explains in great deal how a "rough shadow" works. It's a form of tailing someone with two people. One is an operative who strikes up an acquaintance with the suspect. This person has to have a knack for inspiring trust. The other shadow is an expert at tailing and when the trusting person gives him or her the signal, that shadow becomes obvious about the tailing -- i.e., a rough shadow. The trusty points out the rough shadow and the subject of the tail begins to open up about why someone would want to follow him (or her).

Paul has an operative who is a natural listening ear.
"You just naturally ache to tell her things. My God, every time I go out with that broad, I sit down and start telling her all of my troubles; about the girl that jilted me in my childhood, so that I never got married, and all that stuff."
(p. 186-187)
Once burned, twice shy.