I've been known to poach a recruit on occasion, or just flip him yellow to keep my options open, but I don't throw big bucks at a green unless I really need him. I look at recruits that I know are vulnerable to flipping. As a rule of thumb, recruits outside your 360 are more likely to be targeted. The further out the recruit is, the more likely it is that you only have one CV or even one scout on the recruit. If you really want to keep the recruit, put an extra CV or two on him, or promise a start. Jack up his interest in your school a bit and make it a losing proposition for the poacher. It also helps to have plenty of backups.
I think to make it harder to poach, we just need to get norbert to increase the "compound interest" factor you get when a recruit is green. Right now, it seems that if you flip a guy green with an AC scout in the first cycle, another coach can turn him yellow with an AC scout in the last cycle. The first coach should generate more interest from keeping the guy green all that time. If the AC scout gave you 100 "mythical recruiting interest points", and your total increased by 5% for every cycle you kept him green, that 100 points would be doubled by signing day, so anyone trying to poach you would have to put in twice the effort to get to the same point you are at. That seems reasonable to me.
Currently, I think the very small adjustment is applied to anyone that has put money on the recruit, but I think it might be more balanced if only the coaches who have the recruits' interest (green or yellow) got the buff.
Maybe norbert could look into it? If the adjustment does in fact already exist, the percentages could probably be tweaked in the beta to see how it would work.