If you want to make it harder for AI or other software to remove the watermark, and if the video is varied enough, you could use a displacement mask:
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This example does a good job of showing the kind of content it is and isn't good for; works well for actual video, not for text/screenshots where the screen is predominantly one or two colors.
How to do it in Vegas:
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I don't actually know how well this works at defeating AI, but I would assume it's a lot better than a transparent overlay. I've also read that adding a subtle noise filter to the video will make it a lot harder to remove watermarks, maybe combine both.