You're not thinking like a Soviet military theorist. If the Soviets do have a single bridge they need to defend, what they do isn't simply put out five decoys and watch NATO bomb all six. What they do is more multi-step: first they camouflage the bridge and build a decoy right next to it. That way, the bomber sent after the bridge see's the more visible decoy and hits that. Then the Soviets dismantle the wreckage of the decoy, remove the current camouflage, and replaces it with new camo that makes the bridge look like this:
That way, when NATO does follow up reconnaissance, they see a bridge they believe they have already hit without a span and go "alright! We took out it's span! No way Ivan drives his tanks across that! Scratch it off the target list."
If they have to, the Soviets can then further play to the deception by occasionally throwing fake pontoon bridges over the river nearby and letting NATO bomb that. Throw in some fake air defenses to make it look more convincing or, alternatively, some
real air defenses so as to possibly bag one or more NATO strike fighters. Such moves also further complicates proposed post-target reassessment: "How are Soviet reinforcements and supplies still getting through with that bridge down?!" "We took a look and it turns out they built a pontoon bridge nearby. Don't worry though, we bombed it so things should be good now. They'll probably throw up more pontoon bridges but we'll bomb those too if we have to!"
Now I've mainly used bridges as a detailed example, but the reality is a lot of the essential principles here still works for other things: when leaguring a mechanized column, for example, you camouflage the column and lay out an equal number of more visible decoys nearby so when NATO comes snooping for the mechanized column they were told were by their intel was in the area they see the decoys and bomb them then go back home and report mission success. Moving to an example that involves the use of other then decoys or camouflage completely, one can lay down smoke over roads when your moving convoys across them so they can't be seen
and when your not moving convoys across them so NATO can't be sure (and before you reply, yes this does work against more modern imaging technology: the Soviets developed smoke that carries particulate matter with it so as to blind IR and thermal). These aren't even the tip of the iceberg in examples, but the point here is that you don't simply decoy and hope for the best. You also don't simply camouflage and hope for the best. Camouflage, decoys, smoke, and everything else are merely the tools used to achieve the intent to deceive. What you do is anticipate enemy actions and intentions so as to apply the tools in such a manner so that the enemy see's what he expects to see and subsequently do what you want him to do. It's that kind of sleight of hand that separates workaday deception efforts from real artistry.