Prevent plagiarism after rejecting a paper?

After reading the question What to do if a referee plagiarises the result after rejecting a paper? I wonder what can be done to prevent this.

I also recently got a conference paper rejected with a good (but not very good) idea. Reviewers gave me 2x weak accept and 1x accept and only the meta-reviewer rejected the paper with bogus arguments.

The next conference where I would like to submit is in a few month such that nearly half a year is in between the two submission deadlines of the conferences. I don't know how may people had access to my work and would like to protect my idea.

I can maybe upload it to arXiv now before submitting it to the conference. Some conferences are fine with this as for example ICML

Publication at http://arxiv.org explicitly does not conflict with ICML.

but I am afraid that this can become problematic for other conferences.

What else can I do?