I have the same issue with the barrier, I believed it would keep the part inside as long as it was not marked as a habitat outline. Well, I should have checked earlier I guess. As I won't be able to do anything tomorrow, I've just submitted my habitat anyways and hope the pictures will make up for the mess it becomes when placed down
I think this was my favourite competition so far, I just loved building this and watching the capybaras is some self-care on its own. So thank you for that great idea, it brought me tremendous joy!