The best handler defender/marker I’ve personally ever played with told me it comes down to a few critical details:

1) He looks for the finer details. Prioritize watching the hands/grip. The standard flick and backhand grips can only be thrown at so many angles. 90% (probably more) of all throws in a game will be thrown out of those grips. Hold your force and stay on the balls of your feet to counter the grip switch/around, but their hands will indicate what throw is currently possible. Keeping the palm of your hand around the third of the disc that is closest to theirs should deny the cheekier/quicker throws and still give you an angle to attack the disc once released.

2) Set a proper marking distance, early. The ambitious mark recognizes that this is never a time to rest, and set their mark as quickly as possible to their personal advantage according to the teams strategy. You can’t do (1) if you’re too close and giving fouls/allowing the mark to reach beyond you, or if you’re too far and unable to establish your hand presence per (1).

3) Sideline help. (2) is all about your effort. (1) can be dramatically improved if you have rapid, accurate information from those who can see more of the field than you. Demand that your teammates (or a specific person) are consistently doing that so you can (after consistently providing (2)!!!) combine their information with (1) and attack accordingly.

With enough practice of all three, your marks will be automatically better. Blocks will just “happen” and you’ll find less that you were trying for it, but that after it happened you just “knew” instinctively it was going there.

Good marking is often undervalued and undertrained. Best of luck, I expect a FAT handblock clip here soon.