I would just make sure that it's not been coated / treated. It may be obvious if the seed is a strange colour, but it may need you to scan the small print. Some garden supply places / nurseries will sell it loose and may be able to advise. Otherwise, keep them off it until it is well established. Don't forget that dogs can eat a fair bit of grass as well, so he needs to be kept away from newly sown grass seeds as well.