ANY security/encryption system is breakable, given knowledge, time and
resources.  Rolling Key systems (of which Keeloq is a one way, point to
point implementation) are probably as good as you can get on a PIC.  You
could go a step further and try some of the techniques heavier duty
systems, such as PGP, use.  It will take a lot of time and PIC resource,
and is still breakable.
Even MicroChip admit Keeloq is breakable (at the last seminar I went to).
Ed Todd <edtodd@sni.net>