Any harm in setting the top AND bottom?

That would be more productive than setting just the upper or lower. I liked a foothold at the upper and a 330 at the lower. Lots of doubles.

Thank you Boss.

And there are two meaning to the cross over thing. One for water animals and the other for land animals. If you are going there anyway set some land traps in the area, lot of game crosses over the top to get to the other side. Dirt holes, blind sets, pee sets and snares......jk

Definitely set both where possible, Ohio this gets a bit iffy as it is hard to get a 330 legal sometimes . Not that beaver always use the crossover. I've watched beaver not use the crossover to go from one pool to the next. Quite embarrassing when your standing there watching this when the landowner is next to you after you set traps. Luckily the offenders were caught that night in coming back up the crossover.

Would a snare at the top, set so the live snared beaver doesn't destroy that crossover, boost the chances of a double?

I would think it would be hard to live snare a beaver that wouldn’t destroy the crossover

I would think that a live snared beaver would probably distract the rest from going to the crossover to find the bottom trap. Perhaps if you had some footholds along the dam out of reach of the snared beaver you could pick up doubles that way or if you have funnel spots for 330s/snares.

By snaring the crossover on a slide cable I can preserve the trail and put the catch where I want it...

Look for a very slight crossover on the ends (usually the right hand side as you look upstream) hang a snare if legal there and you will catch some of the biggest beaver in the area on it. I mean slight, literally just a bit slicked down more like a slightly muddy trail