Obviously we need to make it as difficult as possible, but there will always be a way around it. I'm much more comfortable giving my kids some freedom, knowing that it comes with a certain level of trust and expectations, then I am with just trying to block everything that's out there. It exists and it is accessible and by just blocking it without being open with my kids it could just make it more alluring. I look at their phones regularly and talk openly about the pitfalls that exist (all of which they are completely aware of as are most kids would be my guess). Some of these talks are more formal as I establish rules, some are more casual so that it's not something that seems so taboo to them.
In the end I admit that I don't know everything that they do on their phones or devices. I do know that I've had multiple situations where they have come to me and my wife when something came up to varying degrees. I try to be vigilant in watching their behavior and reactions to certain things and if I've had suspicions we talk about it. I feel that making all of these things so taboo and so riddled with shame that kids just learn how to lie and cover their tracks. I try to let them know that they don't need to lie and hide what they are doing and that if they feel like they need to then it's probably not good.
In the end kids have always and will always get into trouble. Technology is the new thing and it's not something I grew up with so it seems scary. But 20, 30, 40, hundreds of years ago kids were getting into trouble. For whatever reason some got into far more trouble than others. It also has continuously gotten easier to do so. I'm sure kids had a much easier time getting into trouble when they started moving into cities, rather than being on the farm like their parents. I don't think it's any different today, they're just using what's available.