Actually, boundaries should be somewhat flexible: gates with a key rather than inpenetrable stone walls that let nothing in or broken fences that let all manner of things through without deterrent. That way you have the control and decide when it is healthy to let someone/something through or when it is safer to keep the gate locked.

You say your boundaries are elastic and porous. Does that mean you are stretching your boundaries uncomfortably or allowing things to happen kind of through osmosis? Is your T saying you have places and situations in your life where you need to firm up those boundaries because yours are too flimsy and creating issues? (Just trying to understand what you are describing about your own boundaries.)