Why "open the case" to switch signals? I'm used to only see final projects to be placed in a case.MOSFET: any small signal n-channel will do for this. BSS138 comes to mind (if you like to test your soldering skills).
If you want to be able to change that with code then you could try to connect that A/D pin also to an Arduino I/O pin. Set the pin when needed to input or to output>low.Leo..
If I use mosfets just to pull it to ground, it wont cause any problems with the signal when it's disconnected right?
Depends on the signals and the rest of the circuit.
Largely the output impedance of the analog signal is of importance, and with it how the particular sensor reacts to having its output shorted to ground (it may not be bothered, it may be killed).You really have to come with concrete sensors and schematics for detailed suggestions.