Well, currently we don't have any kind of notification messages for cards getting sent from the top of deck to the bottom. So Secret Clocktower and other similar cards can be quite easily used for cheating, for example if I look at the top 3 cards, send one to hand and keep the other 2 on top, or send both to bottom. Can a notification for moving cards like that be added?
I don't see an option to send cards to bottom of deck directly when i look at top X cards. I can send them to bottom without showing the opponent which one by setting the card as shield and moving it to bottom from there.
I cast Positron, look at top 4 cards, a window opens. I choose My spell, move it to battle/grave. Now the rest of the 3 spells, I drag to the bottom from the window. When no cards remain in the window, I close it. A message is shown which reads, Mighty has stopped looking at top 1 cards of his deck. (Yes, 1, not 4). Now opponenet has no idea if I dragged them to the bottom or on the top, so yeah. Easily cheatable.
Ok here's the thing. If you look at X cards it will notify "Player looks at top X cards". If you drag Y cards to bottom of deck, then close the window it will notify "Player stops looking at top (X-Y) cards". It doesn't matter how many cards you moved to field or hand, those will not be subtracted, only those moved to bottom of deck will. Therefore it is always possible to know how many cards opponent dragged to bottom of deck from the ones he was looking at.
Technically we should always be moving to bottom of deck from shields only. (Until we have sufficiently automated these cards)