using git-push to backup repo...strange behavior

at least to me.

I have a git repo locally. Want to essentially back it up on a remote server using git.

First step was tar/gz the repo, scp it to my server and expand it. Periodically throughout the day, I will do a

git push ssh://my.hostname.com/path/to/git/repo

There's a few issues:

1. Sometimes it doesn't work, saying a branch is "non fast forward".
--mirror or -f fixes this, but it seems wrong; I make no changes
remotely and clocks are in sync
2. --mirror doesn't like git stash, saying 'stash' is a "funny
refname"
3. On the remote side, I can find no way to update the working dir
with the changes other than git reset --hard.  Do I even need to do
this?  I'd like to be able to for automated builds/tests someday.
4. I made post-update executable, but it never runs (it echos a
message to a file)

I can't help feeling I'm doing everything wrong and just chancing on things working under certain conditions.

Dave