Re: Only once
Golly I've been "fired"* a number of times, and no-one has been quite crazy enough to kick me out without trying to find an acceptable compromise.
If you need someone gone, just offer them a suitably sized sack of cash and go from there. It's also a lot easier to ask them back, or pick their brains, or have them warn you of potential fuck ups if your last interaction was "here's a cheque, now GTFO"
* Usually asked to leave and negotiated, as being dismissed requires more paperwork and leaves a black mark on your record. Plus contracting, so you get asked back a lot, but you're too expensive to keep on payroll.