Hi
This is my first post on the forum, but I have been watching from afar for about 3 years now as I am a good friend of Linea.
Being a fellow landscape designer/contractor, I have come across the same problem myself on several occasions, when I have produced a plan to 'win' a smaller contract, shown the customer my plan, they say they do not like it (or similar) and subsequently get someone else in to construct it to my plan.
I think I may have found the answer today. I was browsing through a uk magazine today http://www.webuser.co.uk and they are reccommending a website http://www.watchdox.com with which you can e-mail the customer your document file in various formats (inc. PDF) and you can choose what privilages they have when viewing it (i.e. enable/disable copy, paste, print and e-mail etc). It can also disable screen prints and the document can be set with a 'life expectancy before it 'expires'.
I am going to try it this week with a SketchUp raised planter design I have produced.
P.s I have checked out your website and was very impressed with your 'artistic' renders of landscape designs. What is the software you use/workflow?