Help with messy drainage

I just started a new flood/drain setup in a 22"x22"x7" propagation tray
The square one gallon pots that i am using are filled with botanicare's readygro
Now the problem is that with flooding and draining about every 3 hours im worried that the medium will drain out of the pots to much and clog things up
should i try to line the bottom of the pots with some kind of mesh or screen to help keep everything in the pot? any other ideas or if it will not really matter that it starts to make a little bit of a mess?

next time use clay pebbels at the bottom .can u not slow it down it sounds like u r feeding them 2 much thats 7 feeds a day u should only feed 3 or 4 times every day.hope everthing goes ok. it sounds like u can get a control valve 2 slow it down a bit. good luck

They sell one gallon paint strainers at the shop I go to.

a knee hi nylon stocking over pots will fix it