walrein is to fragile. the only good defensive thing it has is thick fat. it isn't good in any defense stat except HP, which is useless without defenses. tazzler proves all my points.
Lapras has monster HP so he might be a good choice until you can get a better pokemon. Or if you think the Ice type tips it off the deep end, you can always use Vaporeon which is one of the more useful ones because it naturely learns Acid Armor. I hope this was help.