No filtering won't prevent a determined individual from accessing porn. However, it goes a long way from preventing accidental exposure, which as someone that doesn't want to see porn and as a parent wants keep my children from running across in casual browsing.
That said the only sure porn filter is a personal determination to avoid it. This is only achieved through learning and teaching correct principles and allowing the individual to implement those principles.
Those correct principles are: Viewing porn makes your personal life miserable and ruins your ability to have meaningful and deep relationships (both sexual and non-sexual) with people of the opposite sex.