I hafta agree that cautious and diligent research is the best course of action BEFORE inking on anything in Thai script, (especially so, as you seem to not be able to read a single character of Thai).
Sadly, I've lost count the number of foreigners I've seen here in Bangkok with totally meaningless Thai script tattoos

, but it’s in the hundreds easily

. ..
When I say meaningless; I mean they had abso-tively posi-lutely NO meaning to a native Thai person reading the script

. Some of them I could figure out; as the tattoos were just word for word English to Thai translations (which BTW; usually mean nothing in Thai

), some where their given names spelled in Thai, some were just adjectives/adverbs or verbs, but most of them, even after I puzzled over them and then asked for an explanation of what it meant, ended up being just nonsense.
It is my experience that ANY tattoo which takes a 5 minute explanation loses a lotta the "kewl-ness" factor no matter how “pretty” the script looks or what language it's done in

.
Just a piece of advice; when asking Thais what they think a possible Thai word tattoo means, DON'T lead them to the answer. Given the Thai penchant for pleasant interaction and non-confrontational conversations, most Thais will agree with you rather than telling you the tattoo is gibberish. You need to show them a tattoo and ask them what they think it means. This obviously means you're gonna need either a bilingual Thai or a grasp of more than two-word-tourist-thai, so you can understand what their answer is if they answer you in Thai.
I must say, the fact you misspelled
แข็งแรง does NOT bode well for the outcome of this endeavor

.
I urge extreme caution!!
Still good luck with it. ..

"Whoever said `Money can`t buy you love or joy` obviously was not making enough money." <- quote by Gene $immon$ of the rock group KISS