It's hard to apply the gel as they may fight back, but gassing them is a better bet, unless they have a gasmask. But in that case I guess they may also have a knife, so the gel is still a nogo.
Jesus you folks must have wild roaches in Denmark. Sounds like "don't go out at night" or "make sure your gun is loaded before entering the woods" kind of thing. Stay safe.
Ah yes, our fearsome Danish roaches - the mighty Germanic cockroach, terror of the Nordic regions! These tiny warriors measure a mere 13mm, but their aggressive nature more than makes up for it. If left unchecked, they'll conduct midnight drills in your attic, their tiny jackboots keeping you awake all night. And you better watch out - your whole family could succumb to carbon monoxide poisoning when they fire up their miniature Panzer divisions for their annual invasion of Poland.
To be honest though, I actually had to research cockroaches in Denmark because I've never heard of anyone having problems with them here.