Unfortunately defender won't be able to buy enougth tanks (except perhaps light tanks) to deal with attacker. And there are always danger axis player buys 10 or more fighters (actually they usually end to attact same abandonet/immobilized tanks so I think 5 fighters would be better). I think it is very risky to buy tanks when defending. Perhaps 1 or 2 tanks as JasonC wrote.
Perhaps it is usefull to invest largely to antitank mines? Perhaps improvised reverse slope tactics to make sure he have to risk his heavy tanks to utilize them? Even thougth assaulting axis can deploy some 2500 points (1500 points game), he is able to get "only" 4 or 5 Tigers (considering he buys also infanry). Not expecially much if you think the amount of antitank mines there are waiting.
I usually push agressively forward (with snipers or tankhunter teams) to recon where enemy is attacking. If my opponent keeps his forces close together the rest of batlemap is for me to manouver.
Also I try to purchase mg carrier per zis at-gun (dammit, only 1500 points). Recons should be able to find enemy quite easily thus giving time to debloy my quality antitank assets. Also zis crew should be crack to make sure they debloy 1 min (crack zis AT-gun is rather costly, some 90 points).
For static defense I think that ligth AA -guns (they are very cheap) are better for platoon AT defense than AT-rifles. If nothing else they provide protect against enemy aircrafts.
I have to try to buy heavy artillery spotters when defending. Home-ever, I think 210 mm artyspotters (conscript costs 93, ammo 12) are better than 203 mm (constript costs 160, ammo 20). Perhaps I missed something?
If attacker keeps his infanry relatively close together, it would also be extremely interesting to set a target reference points to somewhere midle of map and utilize a sniper to spot advansing enemy for two (or perhaps three) 300 mm rocket spotters (Unfortunately it requires least 5 rocket spotters to effectively destroy targetarea). Actually, rockets efective area is huge enougth to kill axis soldiers even if they are not deployed very close together.
Rockets may not be effective against tanks but without supporting infanry even superior Tigers cannot do much to occupy victoryflags.