Edit: i.e. landing on a net stretched (under the lake/ocean-surface) by 3 or 4 ships - reel the net it in to raise stage out of the water, I'm pretty sure seawater is not significantly corrosive from 2-3 hours of exposure.
There's a cool mock-up video of what that might look like: https://www.youtube.com/watch?v=4Ca6x4QbpoM
Seawater is incredibly corrosive and as it evaporates it leaves behind a fine layer of sea salt. Since these were SRBs, they had few moving parts. They were completely disassembled and the individual components were inspected and recertified prior to the next launch.
Also, just to give you some scale of how crazy the Space Shuttle program was: the SRBs are the largest lift platform that was ever in use. ICBMs are fireworks compared to them. To land in the water, the SRBs needed not one but 3 of the largest parachutes ever produced.
Some of the parts from the first missions were re used on the last. The SRBs weren't disposable, but they were essentially refurbished after each launch.
Also, there's no land downrange from the launch site, and returning the stage to land at the launch site costs a lot of extra fuel. It is possible and actually planned to do so later (SpaceX is constructing a landing pad for this purpose at the Cape at this time), but for now they are trying to get the ship landings down properly.
Landing on a dry surface means they can eventually reuse rockets soon after landing (a few days I believe).