Question

کار از محکم کاری عیب نمی کنه

Answer 1

Hi

To have two strings to your bow

Answer 2

Better safe than sorry

Answer 3

(just) to be on the safe side
being especially careful in order to avoid something unpleasant:
I'm sure it won't rain, but I'll take an umbrella (just) to be on the safe side (= to be ready if it does rain).

 

From Cambridge Advanced Learner's Dictionary

 

Answer 4

کار از محکم کاری عیب نمیکنه

محکم کاری ضرر نداره

برای محکم کاری

...

Cover your back / ass

to make sure that you cannot be blamed or criticized later for something you have done

Ex: I'm gonna cover my back and get written permission before I go.

http://idioms.thefreedictionary.com/cover+back

 

To keep your back covered

You'd better make a copy of that letter to keep your back covered.

http://www.learn-english-today.com/idioms/idiom-alphalists/alpha-list_K/id_K1-kangaroo-keepno.html