Of course neither the Explorer or the Quatro are "totally" waterproof like the Excallibur, but if your careful you can put the coil under water, just don't get water in the shaft and lift it over your shoulder or get the housing wet, but I own the Quatro, and it's a great machine, everything, everyone say's it is here on the forum. I've never "owned" the Explorer, but I've read the owners manual, and listend to numerous posts on it, and in my opinion, the "main", not the only, but the main difference between that and the Quatro is that the Explorer has two numeric readouts: one for ferrous metal and one for conductive, so, it should give you more information on what the target is in order to make a decision on whether to dig it or not. I believe the Quatro goes as deep or almost as the Explorer, but it starts getting down to some of the extra features, and stuff, like the little light the Explorer has in the housing, and whatever. To me it's like comparing a full featured Honda Accord with an Acura. They're both good, but let's get down to the absolute nitty'gritty, and make a decision. I'd talk to Mike from Virginia Beach if you can, because he's owned and used both, he may even have the CZ70, I'm not sure, but he's got a bunch of past posts here on both of the Minalab units. Good luck, and I think either way, you won't go wrong. Marc.
