I use a ziptie around their legs...not tight, mind you. After everyone has been cleared for egg laying, I can mark them next time by removing their tie. Then all the ones with zipties are the "unmarked for layers" group.
I check them the most thoroughly during peak egg laying months like Feb/Mar. If they aren't laying daily by the end of March, they aren't going to.
I also do a light cull in the fall. By a light cull, I just clear out any birds that didn't lay well in the summer, didn't recover feathers from last year's moult, any barebacked hens. This one is more tricky due to the fact that most birds slow down laying during the moult and this can carry into the fall/winter.
I check them the most thoroughly during peak egg laying months like Feb/Mar. If they aren't laying daily by the end of March, they aren't going to.
I also do a light cull in the fall. By a light cull, I just clear out any birds that didn't lay well in the summer, didn't recover feathers from last year's moult, any barebacked hens. This one is more tricky due to the fact that most birds slow down laying during the moult and this can carry into the fall/winter.