I'm afraid the desire for a bitch in heat is a very strong natural urge. When our mastiff was in heat we had to keep her separate from out (entire) male labrador retriever to avoid an unwanted litter (They would have been
so cute but..!) Della slept in the kitchen and Dyson in the study. Now Dyson isn't elderly, but he has never been the most agile dog, needing help climbing into the car for example. However he managed to scale a bookcase, and cluttered windowsill to climb out of the study window to try and get to Della (
my thread about it here).
I have heard tales of people's front doors destroyed by wandering dogs in search of the interesting bitch within their house...Della is now neutered!
I suspect stronger fencing is a good first step, because you can't really expect the dog to withstand that attraction. It really does make them frantic.
As to walking on leads, I'm not qualified to give advice, because we so rarely do that too. Both our dogs although strong, are very affectionate and after the first excitement are happy to walk close with us. A handful of smelly treats also helps!
One thing that we do with Della even now, since we are rather nervous that she does stray (over, under, through the fence!) is that we attach her to an old tyre with a long chain. She is happy dragging this around most of the time, but would be unable to take it over the fence with her. Obviously we don't just leave her attached to the tyre in case she wraps herself round a tree, or otherwise gets stuck, so she is usually only out for short periods without supervision, and mostly with us and off her chain. Warning- if you do try this, the tyre dragging along the ground erases plants! We never need to trim the vegetation along the paths by the house now.