The reason why the two casters at the layout end do not need locks is because they are lifted off the floor by about 1/4″. This is done to ensure an accurate staging track height to layout track height when the Staging Elevator is in operation.
In the picture above, there is a horizontal beam made of 2×2 and 1×3 poplar. The Staging Elevator (on the right) rides on this. The beam is carefully doweled and bolted to the layout so that it is parallel to the top of the layout (not necessarily parallel to the floor). Therefore, when the Staging Elevator is moved horizontally (what I called transfer-table like motion) it will maintain a good height to allow the locomotives and rolling stock to smoothly go from staging to layout and back again.
The picture above shows how this is done. The beam is just to the lower left of the throttle pocket (black bracket). There is another 1×2 “L” beam on the Staging Elevator where the silver wheel bracket is attached. Originally, I tried running on the layout beam using a fixed wheel in the silver bracket. However, I could not maintain the rail height to the layout tracks consistently as this plastic wheel was out-of-round. The block shown mounted in the former wheel’s axle makes for a consistent height through the range of motion. I applied a pad to the block made from laminated styrene sheets. I also rub some bar hand soap along the beam to lubricate the motion.
There is enough friction with this setup such that no locking means is needed once tracks are aligned by moving the Staging Elevator laterally.