I gotta personally say thank you as well! A few days ago, my one-year-old managed to lock my SA-HT75 player -- was able to unlock it by unplugging it and plugging it back in. However, I really liked that feature, which is nowhere in a manual! I called tech support, and they claimed not to know about it.
After finding your post, I fooled around with it, and realized that locked the tray only. Pressing "PLAY" on the deck and then "POWER" on the remote locks EVERYTHING, including disk skip. (Menu selections still work, which is good)
This is a great feature for someone with a one-year-old that likes to take DVD's out all the time, or change disks on you. Thanks again!!