Licensing furniture and/or selling to stores

i realize this thread is at least a month old, but what I’d really like to know, is how does a designer prevent some company from stealing his designs? eg. they turn you down after your presentation, but then you see a product just like that out in stores later on made by them? i mean does every single idea/product need to be patented before one goes out to market them? that would be incredibly expensive and time consuming i reckon.

any thoughts anyone?