There's a clever invention that you folks in Australia might want to look into. It's been around in this country for a bit-- I think it was developed just prior to WWII using technology that had been evolving since the early 1900s-- and we named it sonar for SOund Navigation And Ranging.
While really expensive at first the technology has been steadily coming down in price until today you can get sonar units for wee boats like ours for a few hundred dollars.
It's a truly astonishing thing. It tells you exactly how far the seabed is from the underside of your hull even though you may not be able to see it looking over the side, and it's far more accurate and, more important, faster than the lead lines I assume you all are using down there currently. And today it's so precise it can measure and display depths that are only two or three feet greater than the depth of you keel. Amazing, really, when you think about it.
I have no idea if sonar, which tends to called a "depth finder" by the amateur boating crowd, has made it down your way yet. But since you all have the Internet now as evidenced by your post above, you might be able to order one on-line from outfits in this country like Defender, Fisheries Supply, West Marine and the like. What's cool is that today sonars can be powered by 12vdc so you don't have to deal with converting from 240vac 50hz to 120vac 60hz.
And even if your government's put the clamps on importing stuff directly from foreign internet retailers, I bet you can find some outfit down there who, if they don't actually have sonar units in stock, can get you one. They may have to launder the device's entry into Australia through another country-- perhaps New Zealand, Indonesia, or Malaysia-- but I'd be willing to bet you could get your hands on one if you asked the right people.
If you do, and if you install it properly on your boat, I suspect you'll find your constant groundings a thing of the past. I said earlier that none of the boaters I know personally have ever gone aground, and this includes some who have been boating for fifty years or so. But all their boats today have sonar, so I bet that's why.
Not long after we got our boat we took our first cruise into BC. We wanted to stay at a great marine park up there but for the life of us we couldn't figure out how to get into the anchorage. It was totally surrounded by very shallow water and even though we had guidebooks and charts we couldn't figure out the way in. We'd nose in toward the anchorage-- we could see boats there-- but every time we were defeated by the bar. But even though we were moving in until my wife on the bow could see the crabs running around in the eelgrass on the bottom we never once touched. Why? Because a previous owner of our boat had installed a sonar. So we could take the boat in until the sonar read three feet or so at which point we'd back away and try someplace else.
So check it out. I think it's a worthwhile addition to any boat.
PS- We have since been shown the way to get into the anchorage I mentioned above but even so we would never attempt it without having the sonar on.