Poop Courtains: If you are annoyed by the opening around the doors at public bathrooms; and are concerned about people identifying you as a pooper. Take a long strip of toilet paper, roll one end and hang it on the openig. This Poop Courtain will give you a sense of security and will make the poop more private.
A-Tuck-n-Slide: when sitting on the pooper, your shoes can give away you identity at anytime. To prevent this from happening, simply tuck your feet backwards and slide them back. Warning: it can cause cramping and is not good on expensive shoes.
Decoy: A person trying come in while you are pooping can be a horrible experience for a shy pooper, to improve your odds simply make a sign that reads "Out of Order" and stick it on the door upon entrance. This sign is not 100% effective but it will divert almost everybody from your stall. Note: dont forget to remove the note after you are done.
I have used these several times, I hope they can help you.