First of all, you need to check spelltooltips ...
If there is concentration required, it would obviously replace the old one.
Then if im not misstaken, prone is automatic concentration loss, so be carefeull when you are jumping.
And finaly, whenever you are hit in combat (if im not misstaken, it should not work for misses) you do automatic constitution roll ... if you fail, your concentration is lost.
So ... basic tip for maintain concentration is High Constitution, High Armor Class, and if possible hiding from enemies (this one depends on how much you need to keep that concentration, and how useless would that character be hidden).
I still dont understand why cant we change Race for our hirelings.

Lets us play Githyanki as racist as they trully are!