I wouldn't say you only want it for 6 months, as Popo says, it will put landlords off. You may only get offered 6 months initially anyway, if they want 12, I would say you just want 6 months to start with just in case of any issues on either side.
We've just done 12 months in two rentals, 6 months in each, as first property went up for sale after 4 months! We've had extensive building work on our house so we had to move out, I also have two teenagers and an elderly dog. This meant we looked for properties that were a bit tired, didn't want a completely minted house, and we paid a double deposit of £2k in case the dog did any damage, although there's more chance of me chewing the furniture than my dog
Take photos when you check in, and thoroughly clean when you leave. We got our first deposit back in full. We move out of the second property tomorrow and I'm going to spend Saturday cleaning, and hopefully will get all my deposit back.