I'm managing a team that's been regularly overachieving (for its reputation stat, at least). The problem I face every year is that there's usually 2-4 players of first team that insist on moving to bigger clubs. It forces me to buy their replacements every year which in turn seriously damages my team chemistry. I tried to counter it by getting more loyal players, but they too seem to complain.
You've not said who you're playing as. If you're FC Nobody in the Faroe Isles, not much you can do. If you're in a lower league in a big country, get promoted a few times and choose the right options when talking to the players. If you're in a decent top-tier league, win it and win or do well in the Champs league.
I'm playing as Warta Poznan, got promoted to Polish top league (which is ranked at three stars in my current game), have won it three times in three years now and once got to a CL final (lost 3-1 to Arsenal ). My rep climbed from 4200 to 5100 during those four years.
I guess there's nothing else I could do to keep them. What if I force some to stay? Will they remain happy if the team's overall morale is v.good+ and we keep winning?
To a certain extent you can stop players from wanting to move by talking to them, but if they're constantly getting courted by big clubs, this is only a temporary fix, and there's no guarantee they'll agree to stay.
Looks like you're close to maxing out your rep for now then (a CL win would of course help). If you're in it for the long haul, what you need to do is help the other Polish teams improve too. You want them to do well in Europe so that the overall league rep will increase. That means spending your money on buying players from the other top Polish teams in the hope that they spend the money wisely and become more competitive in Europe. If you're the only Polish team doing well in Europe, you're the only one improving the Polish league's rep. If they start to get better and thereby increase their rep and raise the Polish league's rankings, players will be happier in Poland in the long term. It will take a while for you to see any real benefits though.
The short term option is to jump ship and move to a bigger league. You can always buy your favourite players from your old club once you're the manager of Real/Barca/Manchester Utd/City/Bayern et al.
Thanks for the insight! Actually, the other clubs seem to be getting richer and performing better on their own, but it's nowhere near a dramatic improvement that would be needed. And I guess I won't be sticking to that game for long enough for that plan to boost the Polish rep to work well. Anyway, thanks for all the help and advice. I guess I will be switching jobs when my contract runs out