I too have no expertise here, but I've known quite a few rodents. So... my amateur take:
I do not think that the area would necessarily need to be cleared of debris first. Rats can get places people would never imagine they could quite easily.
What I did find to be consistent with rodents is the difficulty in getting them to use set search patterns and such. Rodents go where and how rodents go, and I've never found it possible to teach them set routes. They get a whiff and tend to go right at whatever they smelled in contrast to dogs who can be taught to take set routes/patterns.
The "distance from the nose" wouldn't matter. Rodents can often smell stuff that's around a mile away... a few inches of dirt (most landmines are under fewer than 25cm of dirt, anti-tank mines under fewer than 30cm) wouldn't be sufficient to deter them.
Reliably signaling humans depends upon the particular rodent. Rodents have personalities, and they will often make very particular signals to their people in response to particular things. Reliably enough to bet a life on it? Not sure, but I don't think they'd be terrible in that regard.
"1) Rats have short legs and can only be used in a smooth, obstruction free area.
2) Rats cannot be trained to move in a search pattern.
3) Rats have the capacity to detect explosive residue and can apparently be encouraged to do so with food rewards...
4) ...but there is no evidence that rats can respond to explosive residue in a hazardous area reliably.
5) There is no evidence that the method of deployment results in a thorough search of the area.
6) The speed of search sometimes claimed would make thorough search (tiny nose within 10 cms of target) physically impossible.
7) The cost of preparing the area where they are used, then dragging the rat back and forth over it has to be added to training and housing the rats.
8) While a rat may indicate on a hazard, it cannot expose and clear it. The cost of manually excavating and clearing any explosive hazard that the rat signals on must also be added to the total cost of clearance.
9) The ground has to be scalped for them to be dragged across it in a straight line, then safe-lanes for the handlers manually searched and cleared – so the total cost of using the rats includes the cost of an armoured vegetation cutter and a fully equipped demining team to prepare the area in which the rat will search.
10) There is absolutely no evidence that the cost is less than the cost of demining the area using the same assets but without rats.
11) Because the rat cannot be trained to search and indicate in a set way (which a dog can be reliably trained to do) there is no way for a Quality Assurance observer to know whether the rat is paying attention, so no way of knowing whether the rat has done anything of any value at all.
"
Ok, I only skimmed the article, but it sounded a bit forced. And already point 1 in the summary makes me sceptic, because rats can climb pretty well as far as I know. (Otherwise I am no expert, either)
"5. There is no evidence that the method of deployment results in a thorough search of the area."
This is the most technical post, and it will go almost unnoticed.
A cool story about a rat or a dog draws more attention than mines which were missed and maimed people years after searching the field.
Anyways, the author of that piece is a little mad, but in the sense that it is worth serious consideration. TLDR: the rats aren't cost effective and, worst of all, haven't scientifically proved to be effective.
I have no expertise. His arguments sound very plausible though.