Yes, and they were worried about attracting attention since there was something dangerous that the attention could find (the summons). Note that when people bring out the risks and dangers of an enterprise it doesn't automatically mean "This is totally undoable!". If you missed it, I made a pretty long plan that incorporated the gang idea, I just took some measures (prohibit the pangolin from showing himself to the rollers) against the risks that we identified.
Oh sorry, I just genuinely misread that part as "in sight of the shore" for some reason. But going far away from the shore introduces other problems, namely aquatic chakra monsters (probably HUGE) and the fact if something goes wrong it will take ages to get back on land.
I guess the main reason I didn't think the water travel would be safe is that last time we were crossing pretty non-monitored waters from a small country to next and it got pretty dicey anyways. I have this feeling that bigger villages have something way better prepared for borders that they share between themselves. Also, losing pursuit in the Sea sounds harder than losing it on land.
There's also plenty of things we don't know about water travel, should've probably asked Mari about it? Maybe we could get bonuses for water travel since we are from Mist? But then again, Hazou didn't even know how to water walk before the swamp and I think all our genin are more accustomed to traveling in swamp and forest environments than at sea.
Bah, what is done is done. I have to say I have not been this disappointed in my own plan before. Some of my plans do turn to shit (like the Summoners and Sealers for chapter 56) but that's usually after the update has dropped.