lifting mechanism and effect of gearbox on stepper motor accuracy

i am working on project in which i need to place hydrophones in a 2mX2mX1m water tank at exact x,y, z coordinates

for the x and y movements i have a traverse guiding rail (for y movement) which sits on a sort of vehicles on wheels (for x movement). these are driven by stepper motors.

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i now need a lifting mechanism to be put on the vehicle for lifting a load of around 3 kgs vertically

1. Can a rack and pinion mechanism be used for vertical lifting? (the pinion will be fixed above water and rack will move vertically carrying with it the hydrophones).

2. Also if a mount my (0.9 Nm holding torque) stepper motor on to a 3:1 gearbox will i still be able to accurately control the position of the vertical dimension? (precision in order of mm required)

3. And what other lifting mechanisms can be used in which the motor stays out of water?
(keeping in mind that noise should be minimum)