They need a partner that respects their home and acknowledges that being in a relationship with them means sharing and doing tasks together.
Communicating their needs and desires is a great way to protect Gemini's boundaries. Thinking the grass is always greener is a major obstacle for Gemini.
Protecting their boundaries and emotions by not being too accessible should be a priority for Cancers. They should learn to say no occasionally instead of trying to please their partners.
A Leo can protect their boundaries by not idealizing someone early on and setting high expectations. They should also be true to themselves and not dim their light.
Virgos could establish boundaries by stopping themselves from trying to find perfection in flaws.