This is a complicated question. Section 62.101 Subsection C describes the expiration of a duty to register. As you can see from the link below, when the duty expires is very fact intensive.
There are two versions of Indecency with a Child. If the offense involved a 'contact' there is a high probability that the registration is for life. BUT, that depends on which part of Chapter 21 was your husband on probation for exactly.
I think it is absolutely worth seeking the advice of an attorney. Many will give you some time to discuss your concerns and whether or not you can retain their services.
Your husband will never be able to get this case off his record. Having gotten deferred, he is not eligible for an expunction nor for a petition of non-disclosure because of the type of case. The deferred will remain on his record permanently; the only "good" thing is that it is not a conviction.