Hello,
Firstly plaudits on your choice of dog!!

I am very biased.
I have a lakeland cross sprocker ( she looks like a big rough coated fell-type terrier) which is out of working stuff. I will be taking her fishing where ever I am allowed to do so, BUT, she is a working dog and I know she will want to run off, kill rabbits and rats, bark at squirrels and generally be a terrier. I bought her for all these wonderfull vermin controlling qualities so I can't fault her focus in that department. Luckily she is too big to go to ground. If your lakeland pup is a proper working terrier, it will go to ground, that could cause you a few problems.....
If the terrier has the fire ( and proper lakelands are famed for being firey

), in it there is very little you can do to stop it trying destroy vermin, I mean for proper terriers ( not show stock....there's that bias again

), they are "hardwired" to kill small squeaky creatures. If you love working terriers ( as I do) that single minded element of their personality is very endearing. You never know your pup may turn some of your fishing trips into impromptu rat hunts ;-).
As you will of no doubt realised, you will have to "break the dog" to livestock, chickens, ducks, sheep, pigs, cows, goats etc. This is pretty easily done though.
For all her wonderful qualities there are definitely trips when I will be leaving the dog at home, or with family or the missus.
let me know how it goes.
all the very best,
Guy