Backstory: So a while back I made a post about my alpha Merry being aggressive with my newest rat Sam. (Here is that post: http://www.ratforum.com/showthread.php?292193-PLEASE-HELP-post-introduction-aggression ) I followed the advice about moving Sam back into a different room to get Merry to relax, but soon after that Merry got injured (Reference post: http://www.ratforum.com/showthread.php?293513-Favoring-dragging-hind-leg-and-behavior-change ) so then I had three rats in three different cages. After Merry healed up I tried to put him back with Pippin, and he almost immediately started becoming aggressive towards Pip. Would back him into the corner all puffed up and make Pippin scream and fear poop. When I noticed they were being bad I'm the cage I changed to having them try to meet each other again out in the play pen. Merry just kept getting more aggressive and drew blood almost immediately after seeing Pippin (who never tried to fight back at all). I resolved to just moving Merry into a cage alone (the bottom half of the DCN) and letting Pippin and Sam live together in the top half. That arrangement was (and is) going great but I still feel bad having Merry live alone. He seems to be perfectly happy (he also enjoyed people more than the other rats), he has plenty of toys and I'm going to try and start training him soon to keep his mind more occupied. I know there is the option of neuter, but I'm worried that it would just be in vain since he is almost a year old and just started being aggressive towards the cage mate he has had for his whole life. I also can't afford that now (especially if it doesn't for sure help) since Sam just had to have surgery yesterday due to some bad tail degloving (I'm not sure what happened but I came home to that issue after work)So my question is: what can I do to make Merry as comfortable as possible being a lone rat?