Former teacher here. One of the more valuable things is to tankproof the child, ie, get the child to understand the tank is 'mine'---if the child is at or just past the 'mine' stage (the time in which the child naturally learns that word and begins applying it aggressively.) The food is 'mine'. The tank and gear are 'mine', and only mama or papa feeds the fishes, and if something is wrong 'run tell me.' Putting the child in the position of protecting the tank can work...where it comes to the kid's friends. If younger sibs---not so much. If you have a range of ages some of which are too young to understand 'mine,' you are up to fortifying the tank. In that case, a childproof lock on the undercabinet, and on any cabinet, plus, possibly, a meaningful canopy that puts the rim out of reach----and remove ANY moveable chairs from the room that contains the tank. The usual route is floor to chair to tank rim to trouble. If there's nothing to use to get up to tank level, youngsters will usually not have the idea in the first place. At that stage of brain development, the usual mental path is 'see-it, do-it' and if an object is not sitting there giving the kid the idea, the idea does not come. THe imagination to go get a chair from another room is not there unless the child has been in the habit of moving and using said chair---which is generally not a good idea.