Avoiding Warp Combat

There are three types of non-aggression-
In neutral systems only
In all systems
Allow colonization in all systems

You have the first option, you want the second. Also remember that when making treaties you have to select one of the three; just ticking the non-agression checkbox doesn't do anything.

"In Neutral Systems only" seems to be a lot easier to get them to agree too, but what does it mean?

So, in a system with no colonies, we don't fight. But, they could invade my homeworld and wipe out my home system and not have violated the "treaty"?

That's more or less what it means. The idea is you can bar access to your systems, preventing the "move a fleet in past the defenses then break the treaty" problem of SEIV.

If they do enter one of my systems and get shot down for it (like the treaty says), they become displeased and dissolve the treaty. Thus the treaty is meaningless.

Maybe if they marked my systems as systems to avoid? But I don't know how to check that.

P.S.: If that's do-able, a neat treaty element to offer would be banning entry to a specific system or planet. I.E. while the treaty is in effect, the system would be marked 'system to avoid' or the planet would be marked 'minefield'.

EDIT: On further contemplation -- If they were to invade and actually beat me, they might be perfectly happy to continue the treaty. Hasn't happened yet, but it's an interesting thought.