If you really need security consider using the grsecurity patchset¹ and pax². It's possible to patch the Ubuntu default kernel without problems. However understanding and configuring this takes time and patience. There is a great guide on Wikibooks through³
1: http://grsecurity.net/
2: http://pax.grsecurity.net/
3: http://en.wikibooks.org/wiki/Grsecurity