We should be concerned about the tree that's about to fall into our well. It's already happened before with the tree that was standing on the other side; if it happens one more time we'll be totally screwed.
to set up (a house, store, etc.); to build; to have at the ready (e.g. a gun); to hold in preparation (e.g. a camera); to adopt a posture; to assume a stance; to put on an air