HT Enterprises Tip-Up Linemarkers are designed to be attached to your tip-up line as a marker for tip-up depth settings. These linemarkers are great for resetting tip-ups after a catch or false trip and when rebaiting hooks.
HT Enterprises Tip-Up Linemarkers come in packs of six and are red/white in color. These linemarkers measure 1/2" in diameter and are HT part number TULM-6.
There really isn't much out there better and easier for marking your depth on a tip up line. Clip on a weight, drop it to the bottom, raise it to the level you want, put the marker on, and when you set your tip up down, you know you're at the correct depth when the marker is at water level.
I haven't found anything easier. I always have a couple in my pockets of my bibs.