If you think that the IW is hilly and challenging, you want to try Cumbria. The Karrimor Great Trail Challenge was just that but if you are fit, you can hack it. I did and I'm a novice 47 yr old weekend runner!
My dog is my motivator. She runs with me and doesn't let me miss a day. 5K a day and she is happy and I'm grateful for having a reason to go out. I totally aggree with Sue - get a [young/fit] dog if you want to achieve your running goals. Oh and the dog insists on cross-country/trail running so it gets you off the tarmac!