Good question! Ive not read much about that, i have heard that if you have a too deeper sand substrate it can trap and build up anaerobic gas in pockets which when released can hurt your fish and shrimp but you would need to have inches and inches of substrate for that. The only snails i have in my tanks just roam around above the sand/gravel so i cant speak from experience but its not something i would worry about.
I purchased a long glass rod from a website that sells brand new science equipment, its for mixing in flasks etc but i just use it to poke around substrate if i have to