How to always Allow or Block Specific Sites?

Login to Admin Tools, click on Web Exceptions and then you can add any website you want to always Allow or Block.

Web Exceptions apply to all users. If you would like to apply Web Exceptions to only specific users the best way to accomplish this is to add the sites you want Blocked to the Web Exceptions, but instead of choosing Block, recategorize them to Work Related.

Then under the User Accounts you want the sites Blocked for you can Block Work Related, but leave Work Related as Allow for users that you want to be able to access them.