Kathya, you guys have to trust people more. I don't ask for deposits for work and in two years have never been ripped off. I don't give the guy who trims trees a deposit before he starts work, my accountant or any other service person and I don't expect one from clients. I'd only ask for a deposit if I had to buy a huge amount of supplies, special paper, binders, postage, etc., stuff I normally wouldn't have on hand.
I trust that business people are professional, as I am. Some of the people I have done work for are people I've never even met. The guy who did our floors when we renovated our bathroom and upstairs hall didn't ask for a deposit and we were talking about hundreds of dollars of labour and materials.
True you can mark the item draft, pdf it or whatever, but if you don't protect it, they can still take the work and do something with it, if they really wanted to. Even password protection doesn't really protect you; for as little as $45 you can buy a program to crack passwords - see
http://www.lastbit.com/. So the reality is, PDFing, watermarking really isn't going to help if you want to protect your work.
I learned about these programs several years ago in the corporate world when our department manager had a sensitive Excel file that had been password protected to keep it safe and a year later couldn't remember the password. At the time I think I paid $30 US for a brute force cracker and within 3 days we had the password. Around the same time, my husband had a locked Access database and gave the administrator password to a senior manager. They both forgot the password and I gave them a link to download a password cracking program and within 15 minutes they had their password. Either they had a weaker password or ran the program on a more powerful computer (they were in an IT department with more powerful computers, than a mere secretary would have).
I simply have clients sign a contract and expect that they will live up to the terms of the contract.