Is it explosive dog or explosives dog?

I can't seem to find a justification either way for this example. Can anyone help me out? Thank you!

In the context of a bomb-sniffing dog, what grammar rule would justify using the (s)? Is it simply a matter of avoiding confusion? thanks!

Solution 1:

Even though you usually use the singular form of a noun as a modifier before another noun ("night clothes", even though they're for many nights), there are exceptions, of which this is one: you say "explosives dog" and never "explosive dog" to refer to a dog that detects explosives. I guess this is because "explosive dog" means a dog liable to explode.