You can adjust the duration of the password caching in
Unfortunately that does not really improve security in typical usage patterns. If you leave your terminal unlocked (or there's a bug in your web browser / pdf reader / etc. that allows arbitrary code execution) it is easy to escalate to root by doing echo alias sudo="/usr/bin/sudo
"I say we take off; nuke the site from orbit. It's the only way to be sure." - Corporal Hicks, in "Aliens"