> The best thing to do is to define a "sentinel" to go at the start and end of a sentence. For example, a "$" sign, or a NUL byte.

The $ sign would get in the way if people actually use it in conersation, and maybe other things don't like the NUL byte.

Maybe '\x1F' (ASCII Unit Separator) or '\x1E' (ASCII Record Separator) are better candidates?