If you are a hunter and have problems with stealthed mobs, these tricks could help you:
Loremasters have a skill to increase your stealth detection (+2) - Sign of Power: Vigilance, Level: 32, 40m Range. This sign provides you with a heightened vigilance against those who would hide from your gaze. 
Hunters also have Deed: Heightened Senses, Trait: Heightened Senses. Your exceptional senses allow you to track creatures over a greater distance, even if they are using Stealth, and to more easily detect creatures using Stealth. Tooltip: Increased Tracking range, Track stealthed monsters, Increased overall stealth detection
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