If the proper weight (50#) is used smooth is not an issue. They deplete there oxygen long before they drag it out.
First day of setting a colony I will often have a BIG trap set for a back foot on a castor pile/stick/smear. 10 ft of #5 chain on it. Then a number of footholds (on drowners), snares (drowner) and even some bodygrips in the right spot. I can take 2-5 beaver on the first night as the beaver gets in the long chain foothold first. If he can act fairly normal and get in and out of the water it attracts others that get in the blind sets. Clint Locklear's beaver night video taught me this and it works great.
Occasionally I will use the long chain traps in shallow water on a castor mound if I am running low on coni's or have a square-shy beaver. Got to check everyday though. To that end you must have multiple swivels on the trap end. Best when grass is not high to clog up swivels, so spring time here. From Dale Billingsley's video I learned to anchor it out in the water but so it can get well up on shore too. Doing that they often are pretty calm and have not ripped up the area to much.
If you go longer than 10 ft in my experience they wind up on logs. It is a sumbagun to get them off.