This subject has been discussed many times before but....
When at home I:
- chain the trailer to an immovable object
- Wheel clamp one wheel
- remove the other wheel and keep it well away
- Hitch lock (one of the ones that slots into the ball recess)
- Hitch Lock (barrel type built into the hitch)
When trailing, I use the barrel hitch lock which locks it to the ball. After launching I put the wheel clamp on.
Make sure you get a simple to operate wheel clamp. You don't want to be hanging about when you've launched your boat. Like Bruce, I use a Euroclamp, similar to this
. Some of the 3 legged ones are not simple to fit.