Sip active response to attack

[greenpdx]

I can detect attacks and block the IP of the UDP packet. But I want an active response to attacks to the sip server, return malformed headers, pen test the IP for open ports, ....
REGISTER and INVITE responses would be needed.
Ideas;
return the nonce or challenge with very large size to create buffer overflows,
allow and never respond past ACK, force timeout on the the attacker software.
Do you have any other ideas on how to respond to attacks?