If I'm explaining a specific rule to someone. I would like to say that the rule has exceptions. How to choose the correct proposition?

1. This rule is not valid in all cases.
2. This rule is not valid for all cases.

Are these sentences commonly used among native speakers? or Is there more powerful sentence?

Edit: I'm teaching arabic to someone. I need to tell him if he sees a specific character at the end of a word. This word is categorized under "feminine words". But it is not a general rule. It has some exceptions. There are some irregular words.

Thank you,

If I'm explaining a specific rule to someone. I would like to say that the rule has exceptions. How to choose the correct proposition?

1. This rule is not valid in all cases.
2. This rule is not valid for all cases.

Are these sentences commonly used among native speakers? or Is there more powerful sentence?

Edit: I'm teaching Arabic to someone. I need to tell him if he sees a specific character at the end of a word. This word is categorized under "feminine words". But it is not a general rule. It has some exceptions. There are some irregular words.

If I'm explaining a specific rule to someone. I would like to say that the rule has exceptions. How to choose the correct proposition?

1. This rule is not valid in all cases.
2. This rule is not valid for all cases.

Are these sentences commonly used among native speakers? or Is there more powerful sentence?

Thank you,

If I'm explaining a specific rule to someone. I would like to say that the rule has exceptions. How to choose the correct proposition?

1. This rule is not valid in all cases.
2. This rule is not valid for all cases.

Are these sentences commonly used among native speakers? or Is there more powerful sentence?

Edit: I'm teaching arabic to someone. I need to tell him if he sees a specific character at the end of a word. This word is categorized under "feminine words". But it is not a general rule. It has some exceptions. There are some irregular words.

Thank you,