Perry Fewell is the best candidate available.
Aggressive 4-3 style, attacking defense. He even did a decent job when he was the interim head coach with Buffalo a few years ago.
We'd have to fire Pioli because he would never bring in a 4-3 coach, but firing Pioli should be a given anyway.
The answer is Perry Fewell.
"Tact is the ability to tell someone to go to hell in such a way that they look forward to the trip"