How about...?

When working on the land an option to click walls up? Like you have red and blue lines. Creat a red or blue wall so you can see the land lines in the air and from underwater.

Another idea would be to have in the objects list a way to find the objects someone has on your land. Yes it highlights yellow but it is hard to find still.

OMG, LOL, such a simple idea and yet it would be so darn useful!

Let me just talk a second to make sure we're on the same page. Actually, there are lots of ways to implement something like this. I'm assuming that it would be a client side effect, so no actual walls would be built. Only you would be able to see it and only if you had it enabled.

One way, would be to put an option in the view menu next to "Property Lines", but call it something like "Property Boxes". I don't like that name, but it says it. So everywhere you have a property line, it would render a colored, probably transparent wall. Each lot would be surrounded by a multisided box colored the same as it's property lines. This might be difficult on the eyes. I don't know. I'd have to see it to know.

Another way, would be in the land dialog. Have an option like "Show Bounding Box" which would show the same thing, but only for that piece of land. This could be temporary, like the way the Show... button works for objects that sell with the land. Or it could be a toggle.

Not sure how best to implement it, but it would be incredibly useful. I waste a ton of time trying to find the boundaries of my lot and have an elaborate set of tricks that I use to do this. This one feature would solve all of that and I don't think it would be that hard for LL to implement.