Pretty badly, apparently. They did look into parachuting them into the sea and recovering them that way, before going to propulsive landing, but the salt water damage is just too much to deal with.
Could they land it in some huge lake?
Freshwater is probably only marginally better and if anything goes wrong the chances that the debris falls on land is much higher. Unfortunately the Great Lakes are too far north.
They land them on a barge. This was an experiment that might have damaged the barge.
Why would they prefer a lake to solid ground? If there was a fuel budget for return to launch site, they’d do that before flying it into a lake. Hell, they’d land it on a patch of grass before dumping it in water. There’s nothing to be gained by making the rocket wet (or a lake all rocket-y, those things are dirty with soot and stuff). They just weren’t sure that it wouldn’t punch a big fat hole in the ship (plus the ship is needed for Falcon Heavy next week), so they’d rather have the rocket get all seawatery than the ship hole-y. As long as the telemetry comes back, who needs an old rocket? Might still learn something from retrieving it but it’s not worth reflying as this booster was an older version that is rather expensive to refurbish.
You’d have to launch it over a lake, but you’re not allowed to fly the first stage over populated areas so it would have to be a very remote huge lake. That’s quite a limiting set of requirements.
The story I heard was that after splashing down and spending time in the sea, the refurb cost was not much different to a new build cost, possibly even greater.
The solid boosters did, but liquid engines are a whole other ball game.
Do you mean that liquid engines are easier or harder to reuse after being dumped in the sea? Maybe you could elaborate on which difference between solid and liquid engines you're focusing on.