As Jack said, just as you reach the top with the hydraulic system, you should hear a soft clank as the spring-loaded bar swings into place under the top. I usually pull the safety release cord and feel it move, then release it again and listen for the bar to lock back again. If the bar is moving freely, you can be sure it is in the proper place to catch the top if the hydraulic system should fail.
Think about the times you drive past a construction site in the evening. You will frequently see their cranes with a heavy generator or other piece of valuable equipment suspended up in the air overnight to prevent someone from stealing it. Hydraulic systems are designed to support this weight and you are not hurting anything with the top in the full up position.