Assistant manager.

I started a save as unemployed, and in November first season i took over as Celtic boss. I signed Brian McClair as my assistant. Having won the league and cup that season, i resigned in Septemeber (second season). I was then offered the job at Norwich (relegated in first season), even though i was McClair's favoured personel, he wouldnt leave Celtic. Never the less, i won the championship with Norwich and at the start of the third season i was offered the Tottenham job, i took it and this time McClair would leave and join me at Spurs. I won the league and both domestic cups that year.
So although you can be your assitant's favoured personel, it doesnt mean he will always follow you to clubs, but if you get sacked or resigned you can also have your staff follow you out and resign also (a degree of loyalty i suppose).