Use your watch tower, to find things local.It usually tells you how long the invader has left.If the lairs belong to an invader thats not showing tthere is a good chance that the lairs are stale.
Also if you find lairs the same way it should give you an indication of the lairs that are likely to still be active.
I know at some time there is / was a timer for them to time out as well,so you know when they are spent, seen but not available