I remember ちず and チーズ as great example for the elongation bar as well.

That is a good one.

I notice that, among English-speakers, the Japanese vowels that they seem to have the most difficulty in elongating correctly are え and お.

Good example (also coz I used to get it wrong in my written exercises) is ビル and ビール :)

But Nagoyankeeさん, there is one thing I am wondering. I see my little daughter, who is learning from me my native language, that many times she can't hear some accents or letters in the words I say...above all if I am talking to my father and that way the talking speed picks up.
In everyday Japanese, basically when you speak to a friend of yours, how true is a long sound and how much is understood by the context?
I am not that good at English so can't speak about it, but in my language I know that some words when speaking freely and smoothly at a good pace some words might sound different to a non native (I know coz I was told before by my wife).

Interesting question.

I would have to say that nearly 100% of the tme, we don't rely on the context but on the clearly pronounced "regular" and "elongated" syllables to understand each other. Too many groups of words would sound similar if we didn't make that distinction. Vowel sounds count much more in Japanese than in English. As a speaker of a Romance language, I trust that you will be able to appreciate this fact much more than English-speakers.

The only times that I have to depend on the context is when I talk to non-Japanese in Japanese.

I had a new question! I'd feel bad if I made a new thread. There should be a Q&A thread, imo. I don't have anyone to ask Japanese questions. ):

...でも ひみつです だから（is this how you say "so"?) "anyone" (how do you say anyone? would 'だれも' work?) を 教えるな (is this the negative command form? "don't tell!"; my computer turns oshi to that kanji, so )ください.

Does this make any sense?

I broke it up so it would cause less confusion (for me. :) )

Am I close?

There's actually a huge Q&A thread.

I'm not sure what you wanted to say. 　By "...でも", did you want to put something infront of the でも? Or did you want to use でも as a connector "but"?

You cannot ever combine the nice です and the strong negative command 教えるな. It sounds very strange at least to the native ear.

Though I'm not clear on the dot part of the 「...でも」, the following sentences are all correct and natural.

ひみつだからだれにも教えないで。

ひみつです。だからだれにも教えないでください。
＿＿＿＿＿＿＿

masculine, colloquial versions:

ひみつだ。だれにも教えるな。

ひみつだからだれにも教えるな。

LOL. i'm such a tard! i completely overlooked that; i feel terrible for doing so. i'll just ask questions there from now on!

i was going to put "watashi wa [name] desu". and have a elliptical pause with "but" because i wasn't sure how it would work otherwise. I suppose [desu. demo] might? not sure.

thanks, i'll keep that in mind! i forgot how to form complex sentences it's been a few years but i'll probably try to relearn it soon! thanks!