I'm probably gonna get the hell beat out of me by the descriptivists, but here's the rule on that:

If the adjective ends in y and is two syllables long you can drop the y and use er and est. Otherwise you use more and most in front of the adjective.

http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/regcom.htm

Sure, you could use securer or securest, just like you could use pleasurabler and pleasurablest instead of more and most pleasurable.

But you'd be incorrect.

TEd