You can use wet wood or pressure treated lumber or even foil coated acrylic - but the key is that you need to be expecting this, and you put the saw in to by-pass mode.

At that point, it's just another dumb saw that will chop your finger off, but it won't trigger the cartridge, and you can make what ever cuts you need.

The way it tries to determine if it's wet wood / a body part is the capacitance change. Slightly different profile which they can use to make an educated guess (obviously erring on the side of caution).

This is why for some time they would give you a free cartridge if yours triggered on flesh - they wanted the data on there from real-life flesh contact to improve their calculations.