How about this?
1.) You need to hack the first layer of the OP
2.) After a few Minutes you can also hack the UG (exact numbers may vary)
3.) You need to hack three layers to get in the UG with 3 diff hackers (exact numbers may vary)
This would also stop the attackers barreling the UG cause they dont want to kill their hackers and it'd stop UG whoring too.
Feel free to suggest yours.