advice on simple problem

my snails keep crawling into my overflows u-tube. once in they cause a buildup of bubbles behind them and im worried someday itll cause the siphon to break. also when they make it to the other side of the overflow they never get back out and i have to shut it down and get them out. my clownfish has also been sucked through the u-tube twice now. i want to use a piece of screen and rubberband section off the suction end of the tube so no snails and fish can go through it. is window screen( non-metallic) and rubberbands reef safe?

 

You can use a fine eggcrate it will work and look better. the sell it in black

 

Could you use that black plastic gutter guard that comes in a roll? I use it to cover my overflows and its worked great.