This is just another attempt at a band-aid fix for an issue that can easily be stopped, if the BB Gods wanted to.
All players should sign one-year contracts when they join a new team.
Grandfather all players currently on a roster until the next season. Any player on a roster when the new season begins, now has a one-year contract.
Teams have one season to determine what to do with their three draftees. They would be free to list them on the player market or keep them. When the next season begins, last year's draftees have a one-year contract.
Any player bought on the player market would be on your roster for 14 weeks plus the number of days until the next Monday, at which time you would be able to fire or sell him.
This would end day-trading immediately.
Also, it would add a little more realism to a "simulation" that has become more of a "Tycoon" game, which someone else called it in another forum, so I can't take credit for that comment.
I like the idea in theory, but the new player who gets a couple of "bargain" 60k salary players when they first sign up is completely hamstrung. And a full season is too long regardless. The cricket sim battrick had a seven-week contract on signing a player, but I don't remember if you could fire a player during that time or if you were just prevented from re-listing him until that time had passed.
I do think an interesting angle would be to incorporate Hattrick's rule about only being able to list a player you've bought the number of games he's played for your team - though it would need to be tweaked here to be based on the number of minutes played. If that rule were in effect, for example, a team would have to play these players regularly in order to keep listing them at their inflated prices and hoping someone bites.
Of course, the way I'd personally go about it is to just restrict the starting bid amount for newly purchased players, so that if you've only had the player a few weeks, you can list him at $1000, and you wouldn't be able to list a player above what you bought him for until a season or more had passed. That way, a manager who gets a legit bargain can still make a fair profit by selling a player, but the whole "list a player absurdly high" strategy wouldn't be possible or would, at minimum, require holding on to the players for 14 weeks.