If you already have a network/router setup at the house, you just need to extend the range of the wifi. To do so, you can add a wireless access point (WAP). This is how most businesses, hotels, etc. do it. They have access points all over the building to allow customers access to the network.
With Apple specific devices, pair it with an Airport Express and you can go directly from your phone, to the audio system with ease.
Another note, is the access points come in a ton of flavors, which includes versions designed specifically to be used outdoors, and units which are designed specifically for long range use. So, you can run a wire down to the dock and put a WAP right at the dock. Or use a long range version near the back door and see if that gives you good coverage where you need it.
If you do not have a router currently, you should pick one up to go along with it. I would not get a router with integrated wireless if you don't have to as the built in wireless range is likely not going to cover you all the way to where you need it, but... some might.
