previous url stuck and will not go away

when i right click on IE button and go to properties and clear pages viewed there has been on entry that will not go away. It was visited many months ago when we had a neighbors son feed the dog when we were on vacation. It would not be that big a deal to have something stuck there, however my kids want to use that PC and when you type in www.p and any other letters it brings up this porn site the little SOB must have gone to and figured he would erase his tracks by clearing history and page views etc. this one will not go no matter what i do and now i have a PC that i can't let my kids near for fear that they might stumble to this site if they start to type www.p........ and then this porn url comes up in the list of urls visited on the task bar.

Help me please.