How to write warning notice to tenant violate parking rule?

[Lulu Heather]

I have a tenant that keeps parking his two trucks in driveway. Although in his lease contract, there is a restricted driveway-parking clause: "Tenant(s) must park in closed garage at all times, not in the driveway". The former owner of this property advised me to not let tenants park in the driveway because they might break the concrete, so I followed her lease. Moreover, those two trucks of this tenant are really heavy, he's a landscaper and has many tools.

Could you guys give me some ideas how to stop my tenant from parking in the driveway, please? I'm thinking about sending him a warning notice or simply a text message, but I don't want to upset him. Because despite this issue, he is a good tenant. Thank you!