It depends how the business is going.
I've kept hourly rate the same over two years but the monthly/quarterly bonus has improved with the amount of work we do... so instead of a possible £100 a month/£300 a quarter it is now £100 a month/£400 a quarter.
So when employee started target was at a lower level and so was the bonus. Target improved and so has the bonus. I see us having an improved bonus in the summer quarters next year or see below.
If a conny or gutter or one off commercial job comes along that I don't want to be involved in (lazy git

) I might say do this one on your day off (4 days a week remember) and you can have 70/75% of the money as a bonus instead of wages. (Usually works out at £15/20 per hour for him for that one job) But it doesn't count towards the monthly/quarterly bonus.
With a very trusted employee you may offer use of the van privately or at least take home at night (tax and insurance implications, mind).