This rule goes along with sharing manipulatives. I like to teach my students to keep manipulatives in the middle of the space they are working. That way one person doesn't always have the manipulatives in front of them the whole time.
Rule #3 - Be responsible with the manipulatives.
We always talk about making sure we are responsible with the materials. This includes using them in a safe way, not throwing manipulatives, keeping manipulatives on the table or in our work space, etc.