No job is worth breaching an internet policy. No matter how much you delete, they know what you are doing, believe me.
BUT, get a good disk scrubber. Something like Killdisk. It uses an encryption algorithm to delete and rewrite additional data to the erased blocks. Unfortunately, it works on the entire disk not individual files. Another option (for files only) is to use something like Iolo's system mechanic (free use for 30 days) and drag stuff into its incinerator. Set the incinerator to about 10 passes per and be prepared to let it run for a while. Casual recovery of the incinerated data is impossible. Nothing however, can prevent a true expert at data recovery, i.e., The Military, FBI, NSA, etc., from retrieving data. I doubt though, that the NSA would be interested in how many times you've climaxed on the internet. *G*