Brenda's claim that she was exempt from taxation because she had earned no money was unassailable.
no one could ever believe the dentist was arrested because his reputation was unassailable
Adjective: Not open to attack or assault, as by military force, brute strength, or logical argument; not subject to denial or dispute. Example: Shakespeare's genius gives his works an unassailable position in world literature. "No one is more dangerous than he who imagines himself pure in heart: for his purity, by definition, is unassailable." -- James Baldwin
Unassailable means unable to be attacked, questioned, or defeated. It suggests that something is secure or invulnerable.
invincible, impregnable and incontestable.
Unassailable, invulnerable, plenipotent, circumspect, dependable.
The sentence has a lack of punctuation and capitalization at the beginning. Additionally, "Scientists have recently discovered" is an incomplete thought. To improve clarity, it can be revised as: "Scientists have recently discovered that not all genes adhere to predictable Mendelian patterns of inheritance. This has forced them to reexamine some formerly unassailable assumptions."
salable, saleable inhalable, unsalable, unsaleable unassailable, unavailable
invulnerable, indestructible, unconquerable, unbeatable, indomitable, unassailable; impregnable, inviolable; informal bulletproof.
Other words for "impregnable" (synonyms) are: potent, inviolate, unshakable, untouchable, unafraid, strong, secure, conceptive
Hitler felt that his position on the continent was unassailable by Britain, so he felt free to open the second front.
Impregnable has many synonyms. Some examples are invincible, unassailable, inviolable, secure, unattackable and strong. Inexpugnable is a synonym for impregnable, but it just doesn't sound like a word that anyone would ever use.