[Travis]

Unless you're hiring workers at low wages (data entry type stuff), I wouldn't bother filtering the net. It'll create more problems (and cost money) than it solves.

If your employees are fairly reasonable, you should explain the policy to them. Tell them nothing is blocked, but here are the acceptable uses. Then set easily measurable standards that they have to perform up to.

Put this way -- if they're getting the work done, why do you care?