"It's funny that there are people who are good at giving alibis, but it would be better if they first thought of the best alibi they could..." The last sentence means "So that it doesn't hang" literally, but I'm not really sure what it would mean in this context.

si_kano have translated the sentence in english very well... except for the last part though. "sabit" is metaphorical expression to mean "problem" or "trouble" '...para sure na di sasabit" would mean "in order not to get any problem for sure." or "in order not to get into any trouble." here, you would normally hear the expression "sabit!" or "sablay!" often said in funny way. :)