Galleys, ocean travel and open borders

Hey all

Im hoping someone can clear something up for me?

I have a neighbour on a nearby landmass, we just made contact

There is ocean between us, but our cultural borders now touch

I DO NOT want him able to sail galleys over right now- yet we can trade resources despite closed borders now

Am i correct in saying that if i keep my borders closed he can not sail into the ocean on my side?

Cheers