Don't worry about it being locked in salt mode for depth or coin hunting. I have used my CZ's (all different models) for over 20 years and have never experienced a depth loss on silver or copper coins in salt mode on both land and in salt water conditions. However, I have original CZ6a's and a CZ20, so I cannot validate if the newer CZ's experience any depth loss (on coins) while in salt mode.
The salt mode makes it more stable in salt water and wet, salt sand but it is also less sensitive to smaller, lower conductive targets like thin gold rings. On the plus side, for land hunting, it will not be as sensitive to small foil.
One suggestion if you do want to use it as a land hunter is get the 8 inch coil. One of the draw backs of any hard wired unit is you obviously can't change coils.
Not sure if water proof is imperative, or you really just want a rugged, water resistant unit that can stand the elements. If so, a used CZ70 Pro or one of the other splash proof, water resistant CZ's are an excellent value. You then have the added options of it not being locked in salt mode as well as being able to change out coils. The small 5 inch coil on a CZ is deadly at finding deep silver among trash...you just have to go slow and creep along, listening for that repeatable high tone 'tink'