Chess books about Defensive Chess

In general, it is a good idea to defend your pieces, even if they are not currently attacked. This way, many tactical tricks of the opponent won't work. In fact, this approach has an antecedent in the theory of Aron Nimzowitch who referred to it as 'overprotection.' Conversely, if you spot undefended pieces of the opponent, you should think about exploiting the situation with a tactical combination.
Another good idea, when you're facing a dangerous attack from your opponent, is to exchange pieces. This makes the position less complicated and usually gives you more space for your defence. Of course it's best to try to exchange your opponent's most active pieces. This should slow his attack down and give you the possibility to start a dangerous counter-attack.