Kia Sorento 2008: Starter motor replacement due to sand

Whilst my 2008 Kia Sorento diesel is generally very good I am worried that the starter motor has had to be replaced at 25,000 km because of sand intrusion and now at 55,000 km has the same problem. We travel on defined sand tracks and firm beach sand and in my opinion the seal to the bell housing is unsuitable for an off-road vehicle. Kia replaced the first one under warranty and I expect them to do that again, but I am worried what happens when the warranty runs out as I hope to keep the vehicle. Logic tells me there must be a fix, where do you suggest I go from here?