How do you make a website school-unblockable?

I know that it won't stay unblocked forever, but how can I make it so that it isn't automatically blocked.... A really good test is my school district, Palm Beach County School of Florida. Our filter/firewall is the most restrictive and blocking one in all of the South East US.... They send all traffic through a proxy ip (the schools) and then filter everything through that IP through WebSense. They do this so WebSense cannot be altered/deleted, and so not just anyone can connect and if they do, they get filtered... foolproof really. But I ran a website a while back and the first time it was ever accessed on a school computer, before i could even use it, it was blocked... obveously autoblocked. But their was their other site (both were arcades) and it took over 5months to get blocked.... Both sites had meta keyword/descriptions involving games/arcades/etc.... what was different? Can anyone help?

Proxy's get blocked immediately!