In this hypothetical situation the wife is clearly committing a serious sin and damaging their relationship.  If the husband were to force the wife this would further damage the relationship to a point that it might not be reparable.  I can't see this being a good solution.  He would probably be better off fighting the danger of incontinence.  After all, single people do it all the time.

Yes, that's a prudential consideration.  But take that out of the equation for the moment ... to get at the principle.  I'm always more interested in the principles ... and then only later their concrete application to real-life situations ... because otherwise the two can get blurred together.

Let's say I lent my snow shovel to my neighbour a couple of weeks ago (and he signed a rental contract and gave me a key to his house) and he is not returning it.  I am expecting a big snowfall tonight and I am afraid my car is going to be stuck in the driveway if I can't shovel out.  My neighbour is still refusing to give me my shovel when I tell him this.  So I go over, break down his door (enter the house with the key and contract in hand), and take it from him by force.

Now it's a fair analogy.

Not quite ... because I don't have rights over the neighbor's property.  I can't trespass onto his property and take my shovel.  But, obviously if I find it in a public place (say, on the sidewalk), I am entitled to take it back without consulting with him.  After marriage, the husband has the rights over his wife's body (and vice versa).

I get it.  It helped to have Pax Vobis modify the analogy.  That illustrated what you wrote here.

Perhaps this is a simple argument to get across my OP point.  Even if man and woman consent to get married, but there is an impediment, like the intent to not have children, the marriage is not valid.  Flip that on its head.  Even if a husband and wife consent to have sɛҳuąƖ relations, but there is an impediment, like the intent to not have children and the 99% chance it will not occur, according to its opposite, the act is not valid.  Consent of the man and woman prior to marriage did not bring validity, and consent of the man and woman after marriage does not bring validity.  In theory, this should be sound.  

If consent of the spouses to avoid pregnancy with rythm method is morally good, then consent to get married and with the intent to avoid children should also be morally good.  But, it is disapproved by the church.  I can think of many unmarried single catholics who in the same sense meet the four conditions presented by pius xii.  What if they want company in their difficult time?  Why should they be denied such "comfort" comparable to the "comforting of the spouses" mentioned to favor observance of rythm. 

I will tell you why marriage should be denied the single catholic who meets the pius xii four conditions.  The reason why is because God has mercy on the widow and the fatherless.  God has mercy on those single catholics who meet the four conditions.  And, that is why the church has not approved of marriage for them/those who intend not the have children.  And, that is the reason why God does not approve of Rythm.  Continence(which is for all catholics), and a baby(which is for those married), is Gods mercy to the married couple.  Both apply to the married couple because the married couple is divided.  

pax vobis - I think st. paul when he said "for a time" was referring to spouses practicing continence, which means avoiding sex entirely.  And, that it was not for spouses to "for a time" have sex with the intent of avoiding children with 99% accuracy.  If that is the case, then "for a time" unmarried catholics can "comfort" themselves and mirror the "comforting" occurring in catholic marriages.  If it is true that "for a time" we can do this as pius xii says, then "for a time" unmarried catholics can fornicate.  It is that simple.  But, that is not the case.  So, we can not "for a time" practice pius xii rythm.  

Lastly, I have a point to make about how it must have the approval of ones priest.  This is faulty in the sense that a priest does not have the fullness of the sacrament of orders.  It would have to be approval of a bishop, which obviously means for each case.  But, it is not.  Because, a bishop, a successor of the apostles, would never allow for such foolish measures and in turn, sin.  It is for one, impractical to an extreme, and the faith is practical.  And, two, simple ones like myself would learn about these proceedings and would have to publicly reject it and correct the bishop, which would be successful.  The pope has always tried underhand measures against the bishops, and this is in harmony with it.  "Keep it quite, keep it in the confessional".  The serpent is the most cunning of all creatures.  The bishops of the catholic church have been marginalized so much over the centuries, that it is only when they all become heretics that the pope grants them their God given rights.  

Pax vobis - I am pretty sure fornication is the right word.  Because, adultery is only when sɛҳuąƖ misbehavior occurs with someone else's spouse.  I don't think adultery is the word for when two unmarried people have what you might call "proper" intercourse.   

"Questions" like that are why you have a Reputation: +2846/-83. 

Seems to me there ARE times when a husband, forcing himself on his spouse, would be considered rape and I think it happens more frequently than you all want to believe:

There can, however, be good reasons that excuse a husband or wife from rendering this marriage debt, such as adultery of the other spouse, or unreasonable demands (e.g. frequency, intoxication) or grave danger to health or life (e.g. by the possible communication of infectious diseases), or a husband who refuses to perform his duty of supporting his family (Jone, Moral Theology, pp. 557 & 558 ).