I agree with leocharre
. Any compiled Perl script can be decompiled by a good perl hacker, then he will turn around and distribute it freely on some hacker site. Besides, most useful scripts have already been written and are free on the net with a little searching. Just look at the Perl books being pirated out there.
Your best bet is to put a copyright on your work, have your clients sign an agreement not to sell or give your program away, then charge consultant fees for installation, maintenance, training, etc. Give the program for free, but charge for installing/ consulting on it. Free software can have an advantage..... you can put a clause in the software that you are limited in liability to the cost. :-)