best way to learn defense

My son has been learning and practice chess tactics and puzzles. Most of these are about offense instead of defense. During the tournaments I find that if he falls behind at the beginning and the opponent initiates the lethal attacks earlier than him he tends to lose the game due to poor defense. Any suggestions about learning approach to enhance defense skills? 

Looking for Trouble

http://dev.jeremysilman.com/shop/pc/Looking-for-Trouble-Recognizing-and-Meeting-Threats-in-Chess-p3862.htm

The New Art of Defence in Chess by Andy Soltis

https://chessbookreviews.wordpress.com/tag/new-art-of-defence-in-chess/

https://www.chess.com/article/view/quotthe-art-of-defense-in-chessquot-by-andrew-soltis

Secrets of Chess Defence

http://www.gambitbooks.com/pdfs/Secrets_of_Chess_Defence.pdf

How to Defend in Chess by Colin Crouch

https://web.archive.org/web/20140708104148/http://www.chesscafe.com/text/howtodefend.pdf

http://www.gambitbooks.com/pdfs/How_to_Defend_in_Chess.pdf

Practical Chess Defence

http://www.qualitychess.co.uk/ebooks/PracticalChessDefence-excerpt.pdf

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I think defense at that level has more to do with good calculation habits than anything associated with defensive techniques you'll find in a book.

For example one basic defensive idea is trading off the opponent's attacking pieces, or keeping a line closed. Well if the kid is losing in the opening it's not because he didn't trade pieces, it's because his opponent is making threats and the kid is ignoring them.

Yeah, tactic puzzles can mistakenly give you the impression you should be as aggressive as possible and ignore what the opponent can do... and even without tactic puzzles that's a common bad habit for new players (even people who have been playing a while).

Maybe one drill that would help is when solving tactic puzzles, first of all don't move the pieces (I know a lot of tactics are done online where you can move them as you solve). Instead, calculate the entire solution before moving the first piece. And then after the kid believes he has the whole solution, make him write it down in chess notation. That will force the person to think in a concrete sequence of moves by both players.

After the whole solution is written down, then make the first move to solve the tactic puzzle.

(I solved puzzles this way mayself and it helped me become better at calculation).

Oh, and don't take notes, don't write down a few moves then erase or keep looking. Only start writing after everything has been calculated in the head.

Also, some new players don't understand that losing a knight or bishop is nearly the same as losing the game. They think checkmate happens with the queen, and sometimes rooks, so the other pieces don't matter.

So make sure the kid understands that in chess you have to be very greedy! Don't lose even a single pawn. At higher levels even being down one pawn can mean you will lose the game.

(of course sacrifices exist, but new players should develop the habit of not losing material, not even a pawn)