One of the most basic deterrents to any possible attacker is the threat of military action. However, as a pacifist, your military may not be very strong. What you should do in that case is simply lie to them into being discouraged from attacking you, claiming that your military is far stronger than theirs. If they actually take the time to look at your nation, they値l see that this is false, and you値l need to fall back on another tactic, but if they don稚, this simple strategy should work just fine.
A variation on tactic 1 is appealing to them, lying and pretending that you池e the kind of nation they like. See, Santamar hates pacifists. They actually tried (but failed) to invade me once just because they were so fed up with my pacifist ideology. If you want to earn their respect and keep stability between the two of you, publicly adopting pacifism may not be the way to go.