I wouldn't worry about closing the gate until the day you plant. Free range visit poo will be just fine for the plants as the concentration is very low.
Here is basically what I do for the chicken/garden thing.
To the main garden, I relocate a few wheel barrow loads of fresh poo and spread it around and till it in during spring break(march). Then in late april-may, I plant it with the veggies and they do great.
My chickens are in portable coops so at the end of winter, I move their coups to a new location and where the coup was, I just dig little holes and pop in a started zucchini plant. About 9 per coup area.
Then, the following season, I take where the zucchinis were, and plant corn instead. I find the zucchini's do well in fresh stuff and the layers upon layers of straw keep the weeds down. And the corn which sucks up nutrients do better in more aged soil.
Chickens do wonders for amending the soil.