What is another word for activities should be confined...?

It depends on the context, but here are some alternatives for "activities should be confined":

Formal:

* Activities should be restricted to...

* Activities should be limited to...

* Activities should be contained within...

* Activities should be circumscribed to...

Informal:

* Activities should stay within...

* Activities should stick to...

* Activities should focus on...

More specific:

* Activities should be isolated to... (emphasizes separation)

* Activities should be enclosed within... (emphasizes physical boundaries)

* Activities should be kept within... (emphasizes control)

Ultimately, the best word will depend on the specific context and the tone you want to convey.