i'd bet it's snails or slugs, a ring of rock salt (the course big rocks for water softner) around the container will keep them away. or a thick ring of diatamecous earth.i have some seedlings outdoors and some have been eaten any idea how to prevent this?
only problem I had with animal urines is that my dog likes to roll in it.....What Veggiegardener said - wait until they are a foot tall or so & then (tomato) cage them.
I would also add that I'd use some wolf/fox urine around them to deter rabbits & deer.