I have an FT-60 and to my knowledge there's not a "transmit inhibit" function that some other radios have.
You can however program odd splits for each memory channel. The instruction manual gives details on how to do this. You set the receive frequency on the frequency you want to listen on, and program each memory channel to "transmit" on a frequency that the FT-60 cannot transmit on, for example 142.000 or 455.000. (Assuming the radio is not modified for out-of-band transmit.) This would help some on not accidentally transmitting on memory channels. That way if you hit the PTT on one of those memory channels, the radio should display "Error" and not transmit. I'm not sure if it can be programmed this way, but worth a try. For VFO frequencies I don't know of a way to disable accidental transmit.
It's good that you're wanting to take this precaution. Hopefully this helps out some.
Very few of the amateur radios I own have a transmit inhibit function. This is mainly a commercial radio function. You can also program a PL or DCS tone for the transmit side that would stop it from activating another radio or repeater. Check the system you want to monitor to be sure you don't accidently get the tone actually being used.