An interesting dilema. A pristine garden and lawn devoid of wild life or a bit rough round the edges with some biodiversity. My mrs has banned me from treating the lawn as she says it poisons the birds and don't get me started on slow worms .
Like everyone else has said I've always found that runnning 6-7 miles at target pace is the key to running a good half marathon. In the 6 weeks before a half my training plan looks like this:
Monday: 7 miles at HM pace
Wednesday 7 miles at HM pace
Friday: Long run (12 miles)
As far as pacing is concerned I have, learned from the 10k advice given to me by philpub, stick to an even pace and don't try and bank time. Too fast in the first half only leads to a lot of pain and slowing down form about 10miles
You might be interested to note that a 40:28 10k time translated into a 1:28 HM (with a cold) for me earlier this year.