I had a Hitec with a dedicated button on the front for the throttle LOCK purpose. There is also a status sigh on the display telling you the status of the button. Press once and the throttle is in hold next time normal.I may be able to help if I know which radio you are using.
I am using a DX7 and a DX8 normally.
I am really missing the safety feature on the Hitec but wont trade it for the model match on the Spektrum.
Both features would have been the best.