Posted: 27/05/2015 at 19:47
It's the farmer's responsibility to keep his cattle in his field. If you're concerned that the wall is insecure make sure he knows. Also make sure he knows that your young children play in the garden, explain that young cattle are naturally curious creatures and they seem attracted to your garden when your children are playing there.
Explain that rather than risk harm, injury and damage to your family and your property, you're giving him the chance to secure his boundary with proper cattle-proof fencing or substantial repairs to the wall.
You could also mention that your understanding of insurance matters is that, if he has been made aware of problems with the wall and does nothing, his insurance company may not pay out on any public liability claims and he may be personally liable.
You can say all that in the friendliest of ways, but still get your point across.