Of course, there is one type of boundary that people often have for themselves, and that concerns morality or ethics. Then there is of course the Law which sets boundaries on people's actions which most people do not flout.
But the boundaries I'm talking about are spiritual boundaries, boundaries that impact whether we suffer, whether we do things to ourselves that harm us. Because so many of such thoughts and actions reflect the force of our society, reflect our upbringing and life experiences, we feel we cannot separate ourselves from these forces.
But when we come to realize that our suffering is caused by these forces, which have impacted our mind, we realize that we must find a way to free ourselves from these forces, these habit-energies.
The way I have proposed to do that in my writing is to see that these forces, these feelings and perceptions, our cravings, are all a product of our mind in reaction to our life experience. They are therefore not reflective of our true self, which is our heart, our true Buddha nature - they are foreign - and thus we say to them all, one by one, "Not me!" See my posts, "How to Protect Yourself against Psychic Attack" and "Freeing Yourself from the Control of Your Mind," among others.
But many people have a problem with this approach because they cannot separate themselves from their mind, they identify with their ego, which is all they've known their entire life.
Recently, a friend shared with me his approach which is to see all of these feelings and perceptions as coming from an external force, not from within. And that he realized that to protect himself he needed to set up boundaries to keep these negative "foreign" energies away from him. When he becomes aware of such an energy approaching him, he turns to a chant, mantra, or prayer to shut that energy out, creating a positive forcefield around him that does not allow the negative energy to enter his mind.
This requires maintaining a heightened awareness of what is occurring around you and to you. To achieve that, he many times during the day voices a chant, mantra, or prayer to center himself and bring him in touch with his true self and the light of God (Buddha nature, divine essence) within him.
By connecting to your spirituality throughout the day, you are more likely to be aware when these forces arise within you to external stimuli. In part because the force will be experienced as jarring to your system, compared to the peace you experience when you center yourself. And thus you will be able to say, "no," to them and instead seek guidance from your heart on how to respond to the situation at hand. For more on boundaries, see my post "Personal Boundaries as Part of a Buddhist Life."
Choose what works best for you. But it is of the utmost importance to your peace of mind that one way or the other you free yourself from the control of these negative energies that are foreign to your true self and your natural state.