Minecraft – How to get barrier blocks in bedrock edition

My suggestion would be to modify the following variable in the server.properties file:

spawn-protection=999999

Then OP yourself and anyone else you trust to place and destroy blocks. This forces your world (or at least any realistic distance from spawn) to have spawn protection. Blocks cannot be placed or destroyed in this area, unless you're an OP (and at least one OP must be listed in order for it to work).

Note that it is currently not possible to fully prevent the griefing you described above in vanilla without tampering with the user's inventory or use of modding tools.

try this command:
/testfor @p {Riding:{id:Boat}}