Using Tech. Reports to 'protect' IP before presenting unpublished work in a conference The question is in the title, really. It is similar to other questions, such as:
How much information should I divulge about on-going unpublished research at a conference?

However, I am wondering if publishing an internal (i.e. non refereed, etc.) technical report actually protects me from any plagiarism if I should encounter one.

I know people sometimes publish in arxiv for this purpose, but I have two concerns: a. it is not customary for me to do that, and b. I am not sure it is considered 'unpublished' for the sake of publishing in a refereed journal later.

What do you think?

Thanks.
If you main concern is plagiarism, then any mechanism for creating a persistent, externally accessible, date-stamped copy of your work will clearly establish priority: arXiv and institution-specific technical memos each work just as well for this purpose.  When I was a graduate student at MIT, I used to use the CSAIL Technical Report series in exactly the way that you describe.  In computer science, at least, most publication venues seem to have no problem with this type of 'prior publication,' although it is not the same for other fields.

Note, however, that this will not actually stop you from being plagiarized, and may actually increase the chance, since it's another copy of your words out there online. It will, however, make it clear that they are your words and not those of the plagiarist.