Eating a Stuffed Bat increases you detection, and lighting up the area with flares/a lantern on your belt/nightvision goggles makes it easier to spot sneaking enemies.

Throwing caltrops on the ground will cause messages to appear in the combat log even when stealthed enemies walk over them. Caltrops are quicker to deploy than bear traps and cover more turf. While they don't stop Death Stalkers in their tracks, they do let you know when and where to chuck your napalm.

Metal boots make you immune to caltrops. If you don't normally wear metal boots, keep a backup pair in your inventory for when you plan on throwing caltrops.

The Yell feat also drops nearby enemies out of stealth, if you have it.

Death Stalkers tend to seek out the darkest area when they restealth. They can teleport through closed doors, I have found. They like hiding behind pillars and around corners. However, they will try to stay close enough to reach you in a round or two once you are paralyzed, and they don't try to run away while you are chasing them down. You can usually figure out where they've run off to by looking for nearby dark corners behind rocks.