Unfortunately, Russia knows very, very well how to deal with this.
1. all citizens in the conquered territories will need a new id card. That card will be required everywhere. You want to send your kids to school, you need the card. You want to take a subway, you need the card. You want to buy groceries, use the ATM machine, the internet, pay your bills, make a phone call, you need your card.
2. the card will need to be re-validated periodically. At the time you need to make an attestation that you don't know the location of any hidden weapon, or any resistance fighter, or foreign agent, etc. The penalty for lying would be jail.
3. set up a system of informants. The rewards for information don't even have to be monetary, it could be: if you want your brother out of jail, you need to tell us 3 useful pieces of information. We decide what we consider to be useful.
How do I know Russia can do all these things? Because Russia (Soviet Union at the time) conquered my Eastern European country right after WW2, and the resistance was minimal. A country with millions of weapons (WW2 just ended), with forests, mountains, lots of places to hide. Well, guerilla warfare still requires you to eat. You can hide in a forest, but from time to time you need to go down to the village. If one person informs, you're finished.
You think Russia doesn't know how to do what the Soviet Union did in '45-'48? They lost the institutional memory? You haven't been paying attention. Putin is ex-KGB. As we speak, he's putting children (!!) in jail for going to a protest with their parents.
Why didn't this work in Afghanistan ? Because Afghanistan is quite different. People don't live in apartment buildings (well, some do, but most not). They know each other. Internet, subways, grocery stores, are nice, but not essential for many, many people. Informants work both ways. The reprisals from the resistance can be worse than those from the occupiers. Etc, etc. This is not racism. Afghani people are absolutely the same as Ukrainian people, or like me and you. They bleed just as much when you put a bullet in them, and dislike that just as much. But the bullet can come from more places. If the Ukrainian resistance were to have an iota of a chance of success, the resistance fighters should be willing to shoot their compatriots who inform on them. The Taliban were willing to do just that.